diff --git a/composer.json b/composer.json
index f634d1e..afb8e33 100644
--- a/composer.json
+++ b/composer.json
@@ -36,7 +36,23 @@
     },
     "autoload": {
         "psr-4": {
-            "Mailjet\\LaravelMailjet\\": "src/"
+            "Mailjet\\LaravelMailjet\\": "src"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Mailjet\\LaravelMailjet\\Tests\\": "tests"
+        }
+    },
+    "extra": {
+        "laravel": {
+            "providers": [
+                "Mailjet\\LaravelMailjet\\MailjetServiceProvider",
+                "Mailjet\\LaravelMailjet\\MailjetMailServiceProvider"
+            ],
+            "aliases": {
+                "Mailjet": "Mailjet\\LaravelMailjet\\Facades\\Mailjet"
+            }
         }
     },
     "config": {
diff --git a/src/Contracts/CampaignContract.php b/src/Contracts/CampaignContract.php
index 89ac5e7..65eb6b9 100644
--- a/src/Contracts/CampaignContract.php
+++ b/src/Contracts/CampaignContract.php
@@ -1,17 +1,18 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Contracts;
 
 use Mailjet\LaravelMailjet\Model\Campaign;
 
 interface CampaignContract
 {
-
     public function getAllCampaigns(array $filters = null);
 
-    public function findByCampaignId($CampaignId);
+    public function findByCampaignId(string $id);
 
-    public function findByNewsletterId($NewsletterId);
+    public function findByNewsletterId(string $id);
 
-    public function updateCampaign($CampaignId, Campaign $campaign);
-}
\ No newline at end of file
+    public function updateCampaign(string $id, Campaign $campaign);
+}
diff --git a/src/Contracts/CampaignDraftContract.php b/src/Contracts/CampaignDraftContract.php
index fe71d3a..11bdc64 100644
--- a/src/Contracts/CampaignDraftContract.php
+++ b/src/Contracts/CampaignDraftContract.php
@@ -1,35 +1,36 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Contracts;
 
 use Mailjet\LaravelMailjet\Model\CampaignDraft;
 
 interface CampaignDraftContract
 {
-
     public function getAllCampaignDrafts(array $filters = null);
 
-    public function findByCampaignDraftId($CampaignId);
+    public function findByCampaignDraftId(string $id);
 
     public function create(CampaignDraft $campaignDraft);
 
-    public function update($CampaignId, CampaignDraft $campaignDraft);
+    public function update(string $id, CampaignDraft $campaignDraft);
 
-    public function getDetailContent($id);
+    public function getDetailContent(string $id);
 
-    public function createDetailContent($id, $contentData);
+    public function createDetailContent(string $id, array $content);
 
-    public function getSchedule($CampaignId);
+    public function getSchedule(string $id);
 
-    public function scheduleCampaign($CampaignId, $date);
+    public function scheduleCampaign(string $id, string $date);
 
-    public function updateCampaignSchedule($CampaignId, $date);
+    public function updateCampaignSchedule(string $id, string $date);
 
-    public function removeSchedule($CampaignId);
+    public function removeSchedule(string $id);
 
-    public function sendCampaign($CampaignId);
+    public function sendCampaign(string $id);
 
-    public function testCampaign($CampaignId, $recipients);
+    public function testCampaign(string $id, array $recipients);
 
-    public function getCampaignStatus($CampaignId);
-}
\ No newline at end of file
+    public function getCampaignStatus(string $id);
+}
diff --git a/src/Contracts/ContactMetadataContract.php b/src/Contracts/ContactMetadataContract.php
index e73b64d..db1b31d 100644
--- a/src/Contracts/ContactMetadataContract.php
+++ b/src/Contracts/ContactMetadataContract.php
@@ -1,9 +1,6 @@
 <?php
-/*
- * To change this license header, choose License Headers in Project Properties.
- * To change this template file, choose Tools | Templates
- * and open the template in the editor.
- */
+
+declare(strict_types=1);
 
 namespace Mailjet\LaravelMailjet\Contracts;
 
@@ -11,14 +8,13 @@
 
 interface ContactMetadataContract
 {
-
     public function getAll();
 
-    public function get($id);
+    public function get(string $id);
 
-    public function create(ContactMetadata $contactMetadata);
+    public function create(ContactMetadata $metadata);
 
-    public function update($id, ContactMetadata $contactMetadata);
+    public function update(string $id, ContactMetadata $metadata);
 
-    public function delete($id);
-}
\ No newline at end of file
+    public function delete(string $id);
+}
diff --git a/src/Contracts/ContactsListContract.php b/src/Contracts/ContactsListContract.php
index 4a64534..5f4bb9e 100644
--- a/src/Contracts/ContactsListContract.php
+++ b/src/Contracts/ContactsListContract.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Contracts;
 
 use Mailjet\LaravelMailjet\Model\Contact;
@@ -7,20 +9,17 @@
 
 interface ContactsListContract
 {
+    public function create(string $id, Contact $contact, $action = Contact::ACTION_ADDFORCE): array;
 
-    public function create($listId, Contact $contact,
-                           $action = Contact::ACTION_ADDFORCE);
-
-    public function update($listId, Contact $contact,
-                           $action = Contact::ACTION_ADDNOFORCE);
+    public function update(string $id, Contact $contact, $action = Contact::ACTION_ADDNOFORCE): array;
 
-    public function subscribe($listId, Contact $contact, $force = true);
+    public function subscribe(string $id, Contact $contact, bool $force = true): array;
 
-    public function unsubscribe($listId, Contact $contact);
+    public function unsubscribe(string $id, Contact $contact): array;
 
-    public function delete($listId, Contact $contact);
+    public function delete(string $id, Contact $contact): array;
 
-    public function updateEmail($listId, Contact $contact, $oldEmail);
+    public function updateEmail(string $id, Contact $contact, string $oldEmail): array;
 
-    public function uploadManyContactsList(ContactsList $contactsList);
-}
\ No newline at end of file
+    public function uploadManyContactsList(ContactsList $list): array;
+}
diff --git a/src/Contracts/EventCallbackUrlContract.php b/src/Contracts/EventCallbackUrlContract.php
index e795ba1..0e2ec90 100644
--- a/src/Contracts/EventCallbackUrlContract.php
+++ b/src/Contracts/EventCallbackUrlContract.php
@@ -1,19 +1,20 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Contracts;
 
 use Mailjet\LaravelMailjet\Model\EventCallbackUrl;
 
 interface EventCallbackUrlContract
 {
+    public function getAll(): array;
 
-    public function getAll();
-
-    public function get($id);
+    public function get(string $id): array;
 
-    public function create(EventCallbackUrl $eventCallbackUrl);
+    public function create(EventCallbackUrl $url): array;
 
-    public function update($id, EventCallbackUrl $eventCallbackUrl);
+    public function update(string $id, EventCallbackUrl $url): array;
 
-    public function delete($id);
-}
\ No newline at end of file
+    public function delete(string $id): array;
+}
diff --git a/src/Contracts/MailjetServiceContract.php b/src/Contracts/MailjetServiceContract.php
index 95d1da2..bc50558 100644
--- a/src/Contracts/MailjetServiceContract.php
+++ b/src/Contracts/MailjetServiceContract.php
@@ -1,17 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Contracts;
 
+use Mailjet\Client;
+use Mailjet\Response;
+
 interface MailjetServiceContract
 {
+    public function post(array $resource, array $args = [], array $options = []): Response;
 
-    public function post($resource, array $args = [], array $options = []);
-
-    public function get($resource, array $args = [], array $options = []);
+    public function get(array $resource, array $args = [], array $options = []): Response;
 
-    public function put($resource, array $args = [], array $options = []);
+    public function put(array $resource, array $args = [], array $options = []): Response;
 
-    public function delete($resource, array $args = [], array $options = []);
+    public function delete(array $resource, array $args = [], array $options = []): Response;
 
-    public function getClient();
-}
\ No newline at end of file
+    public function getClient(): Client;
+}
diff --git a/src/Contracts/TemplateServiceContract.php b/src/Contracts/TemplateServiceContract.php
index 63493d0..ba7b1d8 100644
--- a/src/Contracts/TemplateServiceContract.php
+++ b/src/Contracts/TemplateServiceContract.php
@@ -1,25 +1,26 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Contracts;
 
 use Mailjet\LaravelMailjet\Model\Template;
 
 interface TemplateServiceContract
 {
+    public function getAll(array $filters = null): array;
 
-    public function getAll(array $filters = null);
-
-    public function get($id);
+    public function get(string $id): array;
 
-    public function create(Template $Template);
+    public function create(Template $template): array;
 
-    public function update($id, Template $Template);
+    public function update(string $id, Template $template): array;
 
-    public function delete($id);
+    public function delete(string $id): array;
 
-    public function getDetailContent($id);
+    public function getDetailContent(string $id): array;
 
-    public function createDetailContent($id, $contentData);
+    public function createDetailContent(string $id, array $content): array;
 
-    public function deleteDetailContent($id);
-}
\ No newline at end of file
+    public function deleteDetailContent(string $id): array;
+}
diff --git a/src/Exception/MailjetException.php b/src/Exception/MailjetException.php
index 8c142fa..9421c5a 100644
--- a/src/Exception/MailjetException.php
+++ b/src/Exception/MailjetException.php
@@ -1,53 +1,55 @@
 <?php
+
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Exception;
 
+use Throwable;
 use \Mailjet\Response;
 
-/**
- * Handle Mailjet API errors
- */
 class MailjetException extends \Exception
 {
-    /**
-     * @var int
-     */
-    private $statusCode;
     /**
      * @var string
      */
     private $errorInfo;
+
     /**
      * @var string
      */
     private $errorMessage;
+
     /**
      * @var string
      */
     private $errorIdentifier;
+
     /**
      * https://dev.mailjet.com/guides/#about-the-mailjet-restful-api
+     *
      * @param Response  $response
      * @param \Throwable $previous
      */
-    public function __construct($statusCode=0, $message=null, Response $response=null, \Throwable $previous=null)
+    public function __construct($statusCode = 0, $message = null, Response $response = null, Throwable $previous = null)
     {
-        // if you pass a Mailjet\Response
         if ($response) {
             $statusCode = $response->getStatus();
-            $message = sprintf('%s: %s', $message, $response->getReasonPhrase());
+            $message = "{$message}: {$response->getReasonPhrase()}";
+
             $this->setErrorFromResponse($response);
         }
+
         parent::__construct($message, $statusCode, $previous);
     }
     /**
-     * Configure MailjetException from Mailjet\Response
-     * @method setErrorFromResponse
+     * Configure MailjetException from Mailjet\Response.
+     *
      * @param  Response $response
      */
-    private function setErrorFromResponse(Response $response)
+    private function setErrorFromResponse(Response $response): void
     {
-        $this->statusCode = $response->getStatus();
         $body = $response->getBody();
+
         if (isset($body['ErrorInfo'])) {
             $this->errorInfo = $body['ErrorInfo'];
         }
@@ -58,24 +60,27 @@ private function setErrorFromResponse(Response $response)
             $this->errorIdentifier = $body['ErrorIdentifier'];
         }
     }
+
     /**
      * @return string
      */
-    public function getErrorInfo()
+    public function getErrorInfo(): string
     {
         return $this->errorInfo;
     }
+
     /**
      * @return string
      */
-    public function getErrorMessage()
+    public function getErrorMessage(): string
     {
         return $this->errorMessage;
     }
+
     /**
      * @return string
      */
-    public function getErrorIdentifier()
+    public function getErrorIdentifier(): string
     {
         return $this->errorIdentifier;
     }
diff --git a/src/Facades/Mailjet.php b/src/Facades/Mailjet.php
index a915abd..f2540e2 100644
--- a/src/Facades/Mailjet.php
+++ b/src/Facades/Mailjet.php
@@ -1,12 +1,14 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Facades;
 
 use Illuminate\Support\Facades\Facade;
 
 class Mailjet extends Facade
 {
-    protected static function getFacadeAccessor()
+    protected static function getFacadeAccessor(): string
     {
         return 'Mailjet';
     }
diff --git a/src/MailjetMailServiceProvider.php b/src/MailjetMailServiceProvider.php
index b8a3a30..c5a1799 100644
--- a/src/MailjetMailServiceProvider.php
+++ b/src/MailjetMailServiceProvider.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet;
 
 use Exception;
diff --git a/src/MailjetServiceProvider.php b/src/MailjetServiceProvider.php
index 043491d..f76875b 100644
--- a/src/MailjetServiceProvider.php
+++ b/src/MailjetServiceProvider.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet;
 
 use Illuminate\Support\ServiceProvider;
@@ -12,7 +14,7 @@ class MailjetServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
     }
 
@@ -21,20 +23,21 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        // Facade
-        $this->app->singleton('Mailjet', function ($app) {
-            $config = $this->app['config']->get('services.mailjet', array());
+        $this->app->singleton('Mailjet', function () {
+            $config = $this->app['config']->get('services.mailjet', []);
             $call = $this->app['config']->get('services.mailjet.common.call', true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
 
             return new MailjetService($config['key'], $config['secret'], $call, $options);
         });
     }
 
-
-    public function provides()
+    /**
+     * @return array
+     */
+    public function provides(): array
     {
         return ['mailjet'];
     }
diff --git a/src/Model/Campaign.php b/src/Model/Campaign.php
index 6f7ddc3..386357b 100644
--- a/src/Model/Campaign.php
+++ b/src/Model/Campaign.php
@@ -1,90 +1,40 @@
 <?php
 
-/*
- * To change this license header, choose License Headers in Project Properties.
- * To change this template file, choose Tools | Templates
- * and open the template in the editor.
- */
+declare(strict_types=1);
 
 namespace Mailjet\LaravelMailjet\Model;
 
 /**
- * https://dev.mailjet.com/email-api/v3/campaign/
+ * https://dev.mailjet.com/email/reference/send-emails/
  */
-class Campaign {
-
-    const FROMEMAIL_KEY = 'FromEmail';
+class Campaign extends Model
+{
+    public const FROM_EMAIL_KEY = 'FromEmail';
 
-    //Mandatory properties (must be set through constructor)
+    /**
+     * @var string
+     */
     protected $fromEmail;
-    //Optional properties (array)
-    protected $optionalProperties = null;
 
     /**
-     * @param $Locale
+     * @param string $fromEmail
+     * @param array  $optionalProperties
      */
-    public function __construct($fromEmail, $optionalProperties = null) {
+    public function __construct(string $fromEmail, array $optionalProperties = [])
+    {
         $this->fromEmail = $fromEmail;
         $this->optionalProperties = $optionalProperties;
     }
 
     /**
-     * Format Campaign for MailJet API request
+     * Format Campaign for MailJet API request.
+     *
      * @return array
      */
-    public function format() {
-
-        /*         * Add the mandatary props* */
-        if (!is_null($this->fromEmail)) {
-            $result[self::FROMEMAIL_KEY] = $this->fromEmail;
-        }
-        /*         * Add the optional props if any* */
-        if (!is_null($this->optionalProperties)) {
-            $result = array_merge($result, $this->optionalProperties);
-        }
-
+    public function format(): array
+    {
+        $result[self::FROM_EMAIL_KEY] = $this->fromEmail;
 
-        return $result;
+        return array_merge($result, $this->optionalProperties);
     }
-
-    /**
-     * Correspond to properties in MailJet request
-     * Array ['PropertyName' => value, ...]
-     */
-    public function getOptionalProperties() {
-        return $this->optionalProperties;
-    }
-
-    /**
-     * Set array of Campaign properties
-     * @param array $properties
-     * @return Properties
-     */
-    public function setOptionalProperties(array $properties) {
-        $this->optionalProperties = $properties;
-        return $this->optionalProperties;
-    }
-
-    /**
-     * Add a new $property to Campaign
-     * @param array $property
-     * @return Properties
-     */
-    public function addOptionalProperty(array $property) {
-        $this->optionalProperties[] = $property;
-        return $this->optionalProperties;
-    }
-
-    /**
-     * Remove a $property from Campaign
-     * @param array $property
-     * @return Properties
-     */
-    public function removeOptionalProperty(array $property) {
-        foreach (array_keys($this->optionalProperties, $property) as $key) {
-            unset($this->optionalProperties[$key]);
-        }
-        return $this->optionalProperties;
-    }
-
 }
diff --git a/src/Model/CampaignDraft.php b/src/Model/CampaignDraft.php
index 659d1a8..bef8dfc 100644
--- a/src/Model/CampaignDraft.php
+++ b/src/Model/CampaignDraft.php
@@ -1,151 +1,133 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Model;
 
 /**
- * https://dev.mailjet.com/email-api/v3/campaigndraft/
+ * https://dev.mailjet.com/email/reference/campaigns/drafts/
  */
-class CampaignDraft {
-
-    const LOCALE_KEY = 'Locale';
-    const SENDER_KEY = 'Sender';
-    const SENDEREMAIL_KEY = 'SenderEmail';
-    const SUBJECT_KEY = 'Subject';
-    const CONTACTLISTID_KEY = 'ContactsListID';
+class CampaignDraft extends Model
+{
+    public const LOCALE_KEY = 'Locale';
+    public const SENDER_KEY = 'Sender';
+    public const SENDER_EMAIL_KEY = 'SenderEmail';
+    public const SUBJECT_KEY = 'Subject';
+    public const CONTACT_LIST_ID_KEY = 'ContactsListID';
 
-    //Mandatory properties (must be set through constructor)
+    /**
+     * @var string
+     */
     protected $locale;
+
+    /**
+     * @var string
+     */
     protected $sender;
-    protected $senderEmail;
-    protected $subject;
-    protected $contactsListID;
-    //Optional properties (array)
-    protected $optionalProperties = null;
-    //content
-    protected $content = null;
-    //id
-    protected $id = null;
 
     /**
-     * @param $Locale
-     * @param $Sender
-     * @param $SenderEmail
-     * @param $Subject
-     * @param $ContactsListID
-     * @param optionalProperties
+     * @var string
      */
-    public function __construct($locale, $sender, $senderEmail, $subject, $contactsListID, $optionalProperties = null) {
-        $this->locale = $locale;
-        $this->sender = $sender;
-        $this->senderEmail = $senderEmail;
-        $this->subject = $subject;
-        $this->contactsListID = $contactsListID;
-        $this->optionalProperties = $optionalProperties;
-    }
+    protected $senderEmail;
 
     /**
-     * Format CampaignDraft for MailJet API request
-     * @return array
+     * @var string
      */
-    public function format() {
-
-        /*         * Add the mandatary props* */
-        if (!is_null($this->locale)) {
-            $result[self::LOCALE_KEY] = $this->locale;
-        }
-
-        if (!is_null($this->sender)) {
-            $result[self::SENDER_KEY] = $this->sender;
-        }
-
-        if (!is_null($this->senderEmail)) {
-            $result[self::SENDEREMAIL_KEY] = $this->senderEmail;
-        }
-        if (!is_null($this->subject)) {
-            $result[self::SUBJECT_KEY] = $this->subject;
-        }
-        if (!is_null($this->contactsListID)) {
-            $result[self::CONTACTLISTID_KEY] = $this->contactsListID;
-        }
-        /*         * Add the optional props if any* */
-        if (!is_null($this->optionalProperties)) {
-            $result = array_merge($result, $this->optionalProperties);
-        }
-
-
-        return $result;
-    }
+    protected $subject;
 
     /**
-     * Correspond to properties in MailJet request
-     * Array ['PropertyName' => value, ...]
+     * @var string
      */
-    public function getOptionalProperties() {
-        return $this->optionalProperties;
-    }
+    protected $contactsListId;
 
     /**
-     * Set array of CampaignDraft properties
-     * @param array $property
-     * @return Properties
+     * @var array|null
      */
-    public function setOptionalProperties(array $properties) {
-        $this->optionalProperties = $properties;
-        return $this->optionalProperties;
-    }
+    protected $content;
 
     /**
-     * Add a new $property to CampaignDraft
-     * @param array $property
-     * @return Properties
+     * @var string|null
      */
-    public function addOptionalProperty(array $property) {
-        $this->optionalProperties[] = $property;
-        return $this->optionalProperties;
+    protected $id;
+
+    public function __construct(string $locale,
+                                string $sender,
+                                string $senderEmail,
+                                string $subject,
+                                string $contactsListId,
+                                array $optionalProperties = [])
+    {
+        $this->locale = $locale;
+        $this->sender = $sender;
+        $this->senderEmail = $senderEmail;
+        $this->subject = $subject;
+        $this->contactsListId = $contactsListId;
+        $this->optionalProperties = $optionalProperties;
     }
 
     /**
-     * Remove a $property from CampaignDraft
-     * @param array $property
-     * @return Properties
+     * Format CampaignDraft for MailJet API request.
+     *
+     * @return array
      */
-    public function removeOptionalProperty(array $property) {
-        foreach (array_keys($this->optionalProperties, $property) as $key) {
-            unset($this->optionalProperties[$key]);
-        }
-        return $this->optionalProperties;
+    public function format(): array
+    {
+        $result = [
+            self::LOCALE_KEY => $this->locale,
+            self::SENDER_KEY => $this->sender,
+            self::SENDER_EMAIL_KEY => $this->senderEmail,
+            self::SUBJECT_KEY => $this->subject,
+            self::CONTACT_LIST_ID_KEY => $this->contactsListId
+        ];
+
+        return array_merge($result, $this->optionalProperties);
     }
 
     /**
-     * Get  CampaignDraft content
-     * @return $content
+     * Get CampaignDraft content.
+     *
+     * @return array|null
      */
-    public function setContent($content) {
-        $this->content = $content;
+    public function getContent(): ?array
+    {
+        return $this->content;
     }
 
     /**
-     * Get  CampaignDraft content
-     * @return $content
+     * Set CampaignDraft content.
+     *
+     * @param $content
+     *
+     * @return \Mailjet\LaravelMailjet\Model\CampaignDraft
      */
-    public function getContent() {
-        return $this->content;
+    public function setContent($content): CampaignDraft
+    {
+        $this->content = $content;
+
+        return $this;
     }
 
     /**
-     * Get  CampaignDraft id
-     * @return $content
+     * Get CampaignDraft id.
+     *
+     * @return string|null
      */
-    public function getId() {
+    public function getId(): ?string
+    {
         return $this->id;
     }
 
     /**
-     * Set  CampaignDraft Id
-     * @return $content
+     * Set CampaignDraft id.
+     *
+     * @param string $id
+     *
+     * @return \Mailjet\LaravelMailjet\Model\CampaignDraft
      */
-    public function setId($id) {
+    public function setId(string $id): CampaignDraft
+    {
         $this->id = $id;
-    }
 
+        return $this;
+    }
 }
diff --git a/src/Model/Contact.php b/src/Model/Contact.php
index cf0543c..32bcb2b 100644
--- a/src/Model/Contact.php
+++ b/src/Model/Contact.php
@@ -1,141 +1,149 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Model;
 
+use RuntimeException;
+
 /**
-* https://dev.mailjet.com/email-api/v3/contactslist-managecontact/
-* Only email is required
-*/
-class Contact
+ * https://dev.mailjet.com/email/reference/contacts/bulk-contact-management/
+ */
+class Contact extends Model
 {
-    const ACTION_ADDFORCE = 'addforce'; # adds the contact and resets the unsub status to false
-    const ACTION_ADDNOFORCE = 'addnoforce'; # adds the contact and does not change the subscription status of the contact
-    const ACTION_REMOVE = 'remove'; # removes the contact from the list
-    const ACTION_UNSUB = 'unsub'; # unsubscribes a contact from the list
+    public const ACTION_ADDFORCE = 'addforce';
+    public const ACTION_ADDNOFORCE = 'addnoforce';
+    public const ACTION_REMOVE = 'remove';
+    public const ACTION_UNSUB = 'unsub';
 
-    const EMAIL_KEY = 'Email';
-    const NAME_KEY = 'Name';
-    const ACTION_KEY = 'Action';
-    const PROPERTIES_KEY = 'Properties';
+    public const EMAIL_KEY = 'Email';
+    public const NAME_KEY = 'Name';
+    public const ACTION_KEY = 'Action';
+    public const PROPERTIES_KEY = 'Properties';
 
+    /**
+     * @var string
+     */
     protected $email;
+
+    /**
+     * @var string|null
+     */
     protected $name;
-    protected $optionalProperties;
+
+    /**
+     * @var string|null
+     */
     protected $action;
 
-    public function __construct($email, array $optionalProperties = [])
+    public function __construct(string $email, array $optionalProperties = [])
     {
         $this->email = $email;
         $this->optionalProperties = $optionalProperties;
     }
 
     /**
-     * Formate contact for MailJet API request
+     * Format Contact for MailJet API request.
+     *
      * @return array
      */
-    public function format()
+    public function format(): array
     {
         $result = [
             self::EMAIL_KEY => $this->email,
+            self::PROPERTIES_KEY => array_filter($this->optionalProperties)
         ];
-        
-        if (!is_null($this->action)) {
-            $result[self::ACTION_KEY] = $this->action;
-        }
 
-        if (!is_null($this->optionalProperties)) {
-            #$result[self::PROPERTIES_KEY] = $this->removeNullProperties($this->properties);
-            $result[self::PROPERTIES_KEY] = $this->optionalProperties;
+        if ($this->action !== null) {
+            $result[self::ACTION_KEY] = $this->action;
         }
 
         return $result;
     }
 
     /**
-     * Correspond to Email in Mailjet request
+     * Correspond to Email in Mailjet request.
      */
-    public function getEmail()
+    public function getEmail(): string
     {
         return $this->email;
     }
 
     /**
-     * Set contact email
+     * Set contact email.
+     *
      * @param string $email
+     *
      * @return Contact
      */
-    public function setEmail($email)
+    public function setEmail($email): Contact
     {
         $this->email = $email;
+
         return $this;
     }
 
     /**
-     * Correspond to Name in MailJet request
+     * Correspond to Name in MailJet request.
      */
-    public function getName()
+    public function getName(): ?string
     {
-        return $this->optionalProperties[self::NAME_KEY];
+        return $this->optionalProperties[self::NAME_KEY] ?? null;
     }
 
     /**
-     * Set contact name
+     * Set contact name.
+     *
      * @param string $name
+     *
      * @return Contact
      */
-    public function setName($name)
+    public function setName(string $name): Contact
     {
         $this->optionalProperties[self::NAME_KEY] = $name;
-        return $this;
-    }
-
-    /**
-     * Correspond to Properties in MailJet request
-     * Array ['property' => value, ...]
-     */
-    public function getProperties()
-    {
-        return $this->optionalProperties;
-    }
 
-    /**
-     * Set array of Contact properties
-     * @param array $properties
-     * @return Contact
-     */
-    public function setProperties(array $properties)
-    {
-        $this->optionalProperties = $properties;
         return $this;
     }
 
     /**
-     * Action to the contact for Synchronization
-     * @return string
+     * Action to the contact for Synchronization.
+     *
+     * @return string|null
      */
-    public function getAction()
+    public function getAction(): ?string
     {
         return $this->action;
     }
 
     /**
-     * Action to the contact for Synchronization
-     * @param string $action ACTION_*
+     * Action to the contact for Synchronization.
+     *
+     * @param string $action (ACTION_* const)
+     *
      * @return Contact
      */
-    public function setAction($action)
+    public function setAction($action): Contact
     {
+        if (! $this->validateAction($action)) {
+            throw new RuntimeException("$action: is not a valid Action.");
+        }
+
         $this->action = $action;
+
         return $this;
     }
 
     /**
-     * Clean null properties to avoid conflict with API
-     * @param  array  $properties
-     * @return array
+     * Validate action.
+     *
+     * @param string $action
+     *
+     * @return bool
      */
-    protected function removeNullProperties(array $properties)
+    protected function validateAction(string $action): bool
     {
-        return array_filter($this->optionalProperties);
+        $available = [self::ACTION_ADDFORCE, self::ACTION_ADDNOFORCE, self::ACTION_REMOVE, self::ACTION_UNSUB];
+
+        return in_array($action, $available);
     }
 }
diff --git a/src/Model/ContactMetadata.php b/src/Model/ContactMetadata.php
index bf51a44..6540f62 100644
--- a/src/Model/ContactMetadata.php
+++ b/src/Model/ContactMetadata.php
@@ -1,39 +1,72 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Model;
 
+use RuntimeException;
+
 /**
-* https://dev.mailjet.com/email-api/v3/contactmetadata/
-* Manage Contact Properties
-*/
-class ContactMetadata
+ * https://dev.mailjet.com/email/reference/contacts/contact-properties/
+ */
+class ContactMetadata implements Requestable
 {
-    const DATATYPE_STR = 'str';
-    const DATATYPE_INT = 'int';
-    const DATATYPE_FLOAT = 'float';
-    const DATATYPE_BOOL = 'bool';
-    const DATATYPE_DATETIME = 'datetime';
+    public const DATATYPE_STR = 'str';
+    public const DATATYPE_INT = 'int';
+    public const DATATYPE_FLOAT = 'float';
+    public const DATATYPE_BOOL = 'bool';
+    public const DATATYPE_DATETIME = 'datetime';
 
+    /**
+     * @var string
+     */
     protected $name;
+
+    /**
+     * @var string
+     */
     protected $datatype;
 
-    public function __construct($name, $datatype)
+    public function __construct(string $name, string $datatype)
     {
+        if (! $this->validateDatatype($datatype)) {
+            throw new RuntimeException("$datatype: is not a valid Datatype.");
+        }
+
         $this->name = $name;
         $this->datatype = $datatype;
     }
 
     /**
-     * Formate contact for Mailjet API request
+     * Format contact for Mailjet API request.
+     *
      * @return array
      */
-    public function format()
+    public function format(): array
     {
-        $result = [
+        return [
             'Name' => $this->name,
             'Datatype' => $this->datatype,
         ];
+    }
+
+    /**
+     * Validate datatype.
+     *
+     * @param string $datatype
+     *
+     * @return bool
+     */
+    protected function validateDatatype(string $datatype): bool
+    {
+        $available = [
+            self::DATATYPE_STR,
+            self::DATATYPE_INT,
+            self::DATATYPE_FLOAT,
+            self::DATATYPE_BOOL,
+            self::DATATYPE_DATETIME,
+        ];
 
-        return $result;
+        return in_array($datatype, $available);
     }
 }
diff --git a/src/Model/ContactsList.php b/src/Model/ContactsList.php
index 45035e4..cd95355 100644
--- a/src/Model/ContactsList.php
+++ b/src/Model/ContactsList.php
@@ -1,32 +1,40 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Model;
 
+use RuntimeException;
+
 /**
-* https://dev.mailjet.com/email-api/v3/contactslist-managemanycontacts/
-* Object to manage many contacts from list
-*/
-class ContactsList
+ * https://dev.mailjet.com/email/reference/contacts/contact-list/
+ */
+class ContactsList extends Model
 {
-    const ACTION_ADDFORCE = 'addforce'; # adds the contact and resets the unsub status to false
-    const ACTION_ADDNOFORCE = 'addnoforce'; # adds the contact and does not change the subscription status of the contact
-    const ACTION_REMOVE = 'remove'; # removes the contact from the list
-    const ACTION_UNSUB = 'unsub'; # unsubscribes a contact from the list
+    public const ACTION_ADDFORCE = 'addforce';
+    public const ACTION_ADDNOFORCE = 'addnoforce';
+    public const ACTION_REMOVE = 'remove';
+    public const ACTION_UNSUB = 'unsub';
 
+    /**
+     * @var string
+     */
     protected $listId;
-    protected $action;
-    protected $contacts;
 
+    /**
+     * @var string
+     */
+    protected $action;
 
     /**
-     * @param int $listId
-     * @param string $action see const ACTION_*
-     * @param array $contacts
+     * @var array
      */
-    public function __construct($listId, $action, $contacts)
+    protected $contacts;
+
+    public function __construct(string $listId, string $action, array $contacts)
     {
-        if (!$this->validateAction($action)) {
-            throw new \RuntimeException("$action: is not a valide Action.");
+        if (! $this->validateAction($action)) {
+            throw new RuntimeException("$action: is not a valid Action.");
         }
 
         $this->listId = $listId;
@@ -35,22 +43,19 @@ public function __construct($listId, $action, $contacts)
     }
 
     /**
-     * Formate contactList for MailJet API request
+     * Format contactList for MailJet API request.
+     *
      * @return array
      */
-    public function format()
+    public function format(): array
     {
         $result = [
             'Action' => $this->action,
-            'Contacts' => [],
         ];
 
-        $contacts = $this->contacts;
-        $contactsArray = array_map(function (Contact $contact) {
+        $result['Contacts'] = array_map(static function (Contact $contact) {
             return $contact->format();
-        }, $contacts);
-
-        $result['Contacts'] = $contactsArray;
+        }, $this->contacts);
 
         return $result;
     }
@@ -58,19 +63,28 @@ public function format()
     /**
      * Get list id
      */
-    public function getListId()
+    public function getListId(): string
     {
         return $this->listId;
     }
 
     /**
-     * Set Action
+     * Get action.
+     */
+    public function getAction(): string
+    {
+        return $this->action;
+    }
+
+    /**
+     * Set action.
+     *
      * @param string $action
      */
-    public function setAction($action)
+    public function setAction($action): ContactsList
     {
-        if (!$this->validateAction($action)) {
-            throw new \RuntimeException("$action: is not a valide Action.");
+        if (! $this->validateAction($action)) {
+            throw new RuntimeException("$action: is not a valid Action.");
         }
 
         $this->action = $action;
@@ -79,32 +93,24 @@ public function setAction($action)
     }
 
     /**
-     * Get action
+     * Get contacts.
      */
-    public function getAction()
-    {
-        return $this->action;
-    }
-
-    /**
-     * Get contacts
-     */
-    public function getContacts()
+    public function getContacts(): array
     {
         return $this->contacts;
     }
 
     /**
-     * Validate if action is authorized
+     * Validate action name.
+     *
      * @param string $action
+     *
      * @return bool
      */
-    private function validateAction($action)
+    protected function validateAction($action): bool
     {
-        $actionAvailable = [self::ACTION_ADDFORCE, self::ACTION_ADDNOFORCE, self::ACTION_REMOVE, self::ACTION_UNSUB];
-        if (in_array($action, $actionAvailable)) {
-            return true;
-        }
-        return false;
+        $actionsAvailable = [self::ACTION_ADDFORCE, self::ACTION_ADDNOFORCE, self::ACTION_REMOVE, self::ACTION_UNSUB];
+
+        return in_array($action, $actionsAvailable);
     }
 }
diff --git a/src/Model/EventCallbackUrl.php b/src/Model/EventCallbackUrl.php
index 1f92dd6..a863973 100644
--- a/src/Model/EventCallbackUrl.php
+++ b/src/Model/EventCallbackUrl.php
@@ -1,85 +1,147 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Model;
 
+use RuntimeException;
+
 /**
-* https://dev.mailjet.com/email-api/v3/eventcallbackurl/
-* Model for EventCallbackUrl
-*/
-class EventCallbackUrl
+ * https://dev.mailjet.com/email/reference/webhook/
+ */
+class EventCallbackUrl implements Requestable
 {
-    const EVENT_TYPE_OPEN = 'open';
-    const EVENT_TYPE_CLICK = 'click';
-    const EVENT_TYPE_BOUNCE = 'bounce';
-    const EVENT_TYPE_SPAM = 'spam';
-    const EVENT_TYPE_BLOCKED = 'blocked';
-    const EVENT_TYPE_UNSUB = 'unsub';
-    const EVENT_TYPE_SENT = 'sent';
+    public const EVENT_TYPE_OPEN = 'open';
+    public const EVENT_TYPE_CLICK = 'click';
+    public const EVENT_TYPE_BOUNCE = 'bounce';
+    public const EVENT_TYPE_SPAM = 'spam';
+    public const EVENT_TYPE_BLOCKED = 'blocked';
+    public const EVENT_TYPE_UNSUB = 'unsub';
+    public const EVENT_TYPE_SENT = 'sent';
 
+    public const EVENT_STATUS_DEAD = 'dead';
+    public const EVENT_STATUS_ALIVE = 'alive';
 
-    const EVENT_STATUS_DEAD = 'dead';
-    const EVENT_STATUS_ALIVE = 'alive';
+    /**
+     * @var string|null
+     */
+    protected $apiKeyId;
 
-    protected $apikeyId;
+    /**
+     * @var string
+     */
     protected $url;
-    protected $eventType;
-    protected $isBackup;
+
+    /**
+     * @var string
+     */
+    protected $type;
+
+    /**
+     * @var string
+     */
     protected $status;
-    // seems to be a problem between API and UI for Mailjet EventCallbackUrl
-    // In the UI when I check the groupEvent checkbox the version=2 when I unchecked
-    // version=1...
-    // And no properties groupEvent in the API reference and here is the description
-    // for version property: Event API version for which this URL is valid.
-    protected $version;
-    protected $groupEvent;
 
+    /**
+     * @var bool
+     */
+    protected $isBackup;
 
+    /**
+     * @var int
+     */
+    protected $version;
 
     /**
-     * @param string $apikeyId
-     * @param string $url
-     * @param string $eventType
-     * @param bool   $isBackup
-     * @param string $status
-     * @param int    $version
-     * @param bool   $groupEvent
+     * @var bool
      */
-    public function __construct($url, $eventType = self::EVENT_TYPE_OPEN, $groupEvent = false,
-                                $isBackup = false, $status = self::EVENT_STATUS_ALIVE,
-                                $version = 1, $apikeyId = null
+    protected $groupEvent;
+
+    public function __construct($url,
+                                $type = self::EVENT_TYPE_OPEN,
+                                $groupEvent = false,
+                                $isBackup = false,
+                                $status = self::EVENT_STATUS_ALIVE,
+                                $version = 1,
+                                $apiKeyId = null
     ) {
+        if (! $this->validateType($type)) {
+            throw new RuntimeException("$type: is not a valid event type.");
+        }
+
+        if (! $this->validateStatus($status)) {
+            throw new RuntimeException("$status: is not a valid event status.");
+        }
+
         $this->url = $url;
-        $this->eventType = $eventType;
+        $this->type = $type;
         $this->isBackup = $isBackup;
         $this->status = $status;
         $this->version = $version;
-        $this->apikeyId = $apikeyId;
+        $this->apiKeyId = $apiKeyId;
         $this->groupEvent = $groupEvent;
     }
 
     /**
-     * Formate contactList for MailJet API request
+     * Format contactList for MailJet API request.
+     *
      * @return array
      */
-    public function format()
+    public function format(): array
     {
         if ($this->groupEvent) {
-            // ugly fix for misunderstanding of this...
+            // Events are grouped only in API version 2.
             $this->version = 2;
         }
 
         $result = [
             'Url' => $this->url,
-            'EventType' => $this->eventType,
-            'IsBackup'  => $this->isBackup,
-            'Status'    => $this->status,
-            'Version'   => $this->version
+            'EventType' => $this->type,
+            'IsBackup' => $this->isBackup,
+            'Status' => $this->status,
+            'Version' => $this->version,
         ];
 
-        if($this->apikeyId){
-            $result['APIKeyID'] = $this->apikeyId;
+        if ($this->apiKeyId) {
+            $result['APIKeyID'] = $this->apiKeyId;
         }
 
         return $result;
     }
+
+    /**
+     * Validate event type.
+     *
+     * @param string $type
+     *
+     * @return bool
+     */
+    protected function validateType(string $type): bool
+    {
+        $available = [
+            self::EVENT_TYPE_OPEN,
+            self::EVENT_TYPE_CLICK,
+            self::EVENT_TYPE_BOUNCE,
+            self::EVENT_TYPE_SPAM,
+            self::EVENT_TYPE_BLOCKED,
+            self::EVENT_TYPE_UNSUB,
+            self::EVENT_TYPE_SENT,
+        ];
+
+        return in_array($type, $available);
+    }
+
+    /**
+     * Validate event status.
+     *
+     * @param string $status
+     *
+     * @return bool
+     */
+    protected function validateStatus(string $status): bool
+    {
+        $available = [self::EVENT_STATUS_ALIVE, self::EVENT_STATUS_DEAD];
+
+        return in_array($status, $available);
+    }
 }
diff --git a/src/Model/Model.php b/src/Model/Model.php
new file mode 100644
index 0000000..f3e040a
--- /dev/null
+++ b/src/Model/Model.php
@@ -0,0 +1,75 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Model;
+
+abstract class Model implements Requestable
+{
+    /**
+     * @var array
+     */
+    protected $optionalProperties;
+
+    /**
+     * Format MailJet API request.
+     *
+     * @return array
+     */
+    abstract public function format(): array;
+
+    /**
+     * Correspond to properties in MailJet request.
+     * Array ['PropertyName' => value, ...]
+     *
+     * @return array
+     */
+    public function getOptionalProperties(): array
+    {
+        return $this->optionalProperties;
+    }
+
+    /**
+     * Set array of optional properties.
+     *
+     * @param array $properties
+     *
+     * @return array
+     */
+    public function setOptionalProperties(array $properties): array
+    {
+        $this->optionalProperties = $properties;
+
+        return $this->optionalProperties;
+    }
+
+    /**
+     * Add a new optional property.
+     *
+     * @param array $property
+     *
+     * @return array
+     */
+    public function addOptionalProperty(array $property): array
+    {
+        $this->optionalProperties[] = $property;
+
+        return $this->optionalProperties;
+    }
+
+    /**
+     * Remove a optional property.
+     *
+     * @param array $property
+     *
+     * @return array
+     */
+    public function removeOptionalProperty(array $property): array
+    {
+        foreach (array_keys($this->optionalProperties, $property) as $key) {
+            unset($this->optionalProperties[$key]);
+        }
+
+        return $this->optionalProperties;
+    }
+}
diff --git a/src/Model/Requestable.php b/src/Model/Requestable.php
new file mode 100644
index 0000000..4e384c6
--- /dev/null
+++ b/src/Model/Requestable.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Model;
+
+interface Requestable
+{
+    /**
+     * Format MailJet API request.
+     *
+     * @return array
+     */
+    public function format(): array;
+}
diff --git a/src/Model/Template.php b/src/Model/Template.php
index d1d6376..f17c3bf 100644
--- a/src/Model/Template.php
+++ b/src/Model/Template.php
@@ -1,122 +1,94 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Model;
 
 /**
- * Description of Template
- *
+ * https://dev.mailjet.com/email/reference/templates
  */
-class Template {
-
-    const NAME_KEY = 'Name';
-
-    //Mandatory properties (must be set through constructor)
-    protected $name;
-    //Optional properties (array)
-    protected $optionalProperties = null;
-    //content
-    protected $content = null;
-    //id
-    protected $id = null;
+class Template extends Model
+{
+    public const NAME_KEY = 'Name';
 
     /**
-     * @param $name
-     * @param optionalProperties
+     * @var string
      */
-    public function __construct($name, $optionalProperties = null) {
-        $this->name = $name;
-        $this->optionalProperties = $optionalProperties;
-    }
+    protected $name;
 
     /**
-     * Format Template for MailJet API request
-     * @return array
+     * @var array|null
      */
-    public function format() {
-
-        /*         * Add the mandatary props* */
-        if (!is_null($this->name)) {
-            $result[self::NAME_KEY] = $this->name;
-        }
-
-        /*         * Add the optional props if any* */
-        if (!is_null($this->optionalProperties)) {
-            $result = array_merge($result, $this->optionalProperties);
-        }
-
-
-        return $result;
-    }
+    protected $content;
 
     /**
-     * Correspond to properties in MailJet request
-     * Array ['PropertyName' => value, ...]
+     * @var string|null
      */
-    public function getOptionalProperties() {
-        return $this->optionalProperties;
-    }
+    protected $id;
 
-    /**
-     * Set array of Template properties
-     * @param array $property
-     * @return Properties
-     */
-    public function setOptionalProperties(array $properties) {
-        $this->optionalProperties = $properties;
-        return $this->optionalProperties;
+    public function __construct(string $name, array $optionalProperties = [])
+    {
+        $this->name = $name;
+        $this->optionalProperties = $optionalProperties;
     }
 
     /**
-     * Add a new $property to Template
-     * @param array $property
-     * @return Properties
+     * Format Template for MailJet API request.
+     *
+     * @return array
      */
-    public function addProperty(array $property) {
-        $this->optionalProperties[] = $property;
-        return $this->optionalProperties;
-    }
+    public function format(): array
+    {
+        $result[self::NAME_KEY] = $this->name;
 
-    /**
-     * Remove a $property from Template
-     * @param array $property
-     * @return Properties
-     */
-    public function removeProperty(array $property) {
-        foreach (array_keys($this->optionalProperties, $property) as $key) {
-            unset($this->optionalProperties[$key]);
-        }
-        return $this->optionalProperties;
+        return array_merge($result, $this->optionalProperties);
     }
 
     /**
      * Get  Template content
-     * @return $content
+     *
+     * @return array|null $content
      */
-    public function setContent($content) {
-        $this->content = $content;
+    public function getContent(): ?array
+    {
+        return $this->content;
     }
 
     /**
-     * Get  Template content
-     * @return $content
+     * Set Template content.
+     *
+     * @param array $content
+     *
+     * @return \Mailjet\LaravelMailjet\Model\Template
      */
-    public function getContent() {
-        return $this->content;
+    public function setContent(array $content): Template
+    {
+        $this->content = $content;
+
+        return $this;
     }
 
     /**
-     * Get Id
-     * @return $content
+     * Get id.
+     *
+     * @return string|null
      */
-    public function getId() {
+    public function getId(): ?string
+    {
         return $this->id;
     }
 
     /**
-     * Set Id
+     * Set id.
+     *
+     * @param string $id
+     *
+     * @return \Mailjet\LaravelMailjet\Model\Template
      */
-    public function setId($id) {
+    public function setId(string $id): Template
+    {
         $this->id = $id;
-    }
 
+        return $this;
+    }
 }
diff --git a/src/Providers/CampaignDraftServiceProvider.php b/src/Providers/CampaignDraftServiceProvider.php
index 81eec0e..d0de3dc 100644
--- a/src/Providers/CampaignDraftServiceProvider.php
+++ b/src/Providers/CampaignDraftServiceProvider.php
@@ -1,13 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Providers;
 
 use Illuminate\Support\ServiceProvider;
-use Mailjet\LaravelMailjet\Services\CampaignDraftService;
 use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\LaravelMailjet\Services\CampaignDraftService;
+use Mailjet\LaravelMailjet\Contracts\CampaignDraftContract;
 
 class CampaignDraftServiceProvider extends ServiceProvider
 {
+    /**
+     * Indicates if loading of the provider is deferred.
+     *
+     * @var bool
+     */
     protected $defer = true;
 
     /**
@@ -15,9 +23,8 @@ class CampaignDraftServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
-        
     }
 
     /**
@@ -25,14 +32,15 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        $this->app->bind('Mailjet\LaravelMailjet\Contracts\CampaignDraftContract',
-            function($app) {
-            $config  = $this->app['config']->get('services.mailjet', array());
-            $call    = $this->app['config']->get('services.mailjet.common.call',true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
-            $mailjetService=new MailjetService($config['key'], $config['secret'], $call,$options);
+        $this->app->bind(CampaignDraftContract::class, function () {
+            $config = $this->app['config']->get('services.mailjet', []);
+            $call = $this->app['config']->get('services.mailjet.common.call', true);
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
+
+            $mailjetService = new MailjetService($config['key'], $config['secret'], $call, $options);
+
             return new CampaignDraftService($mailjetService);
         });
     }
@@ -42,8 +50,8 @@ function($app) {
      *
      * @return array
      */
-    public function provides()
+    public function provides(): array
     {
-        return ['Mailjet\LaravelMailjet\Contracts\CampaignDraftContract'];
+        return [CampaignDraftContract::class];
     }
-}
\ No newline at end of file
+}
diff --git a/src/Providers/CampaignServiceProvider.php b/src/Providers/CampaignServiceProvider.php
index 0631998..150cf6c 100644
--- a/src/Providers/CampaignServiceProvider.php
+++ b/src/Providers/CampaignServiceProvider.php
@@ -1,13 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Providers;
 
 use Illuminate\Support\ServiceProvider;
-use Mailjet\LaravelMailjet\Services\CampaignService;
 use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\LaravelMailjet\Services\CampaignService;
+use Mailjet\LaravelMailjet\Contracts\CampaignContract;
 
 class CampaignServiceProvider extends ServiceProvider
 {
+    /**
+     * Indicates if loading of the provider is deferred.
+     *
+     * @var bool
+     */
     protected $defer = true;
 
     /**
@@ -15,9 +23,8 @@ class CampaignServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
-
     }
 
     /**
@@ -25,14 +32,15 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        $this->app->bind('Mailjet\LaravelMailjet\Contracts\CampaignContract',
-            function($app) {
-            $config  = $this->app['config']->get('services.mailjet', array());
-            $call    = $this->app['config']->get('services.mailjet.common.call',true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
-            $mailjetService=new MailjetService($config['key'], $config['secret'], $call,$options);
+        $this->app->bind(CampaignContract::class, function () {
+            $config = $this->app['config']->get('services.mailjet', []);
+            $call = $this->app['config']->get('services.mailjet.common.call', true);
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
+
+            $mailjetService = new MailjetService($config['key'], $config['secret'], $call, $options);
+
             return new CampaignService($mailjetService);
         });
     }
@@ -42,8 +50,8 @@ function($app) {
      *
      * @return array
      */
-    public function provides()
+    public function provides(): array
     {
-        return ['Mailjet\LaravelMailjet\Contracts\CampaignContract'];
+        return [CampaignContract::class];
     }
-}
\ No newline at end of file
+}
diff --git a/src/Providers/ContactMetadataServiceProvider.php b/src/Providers/ContactMetadataServiceProvider.php
index 10bce5b..38d3cff 100644
--- a/src/Providers/ContactMetadataServiceProvider.php
+++ b/src/Providers/ContactMetadataServiceProvider.php
@@ -1,13 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Providers;
 
 use Illuminate\Support\ServiceProvider;
-use Mailjet\LaravelMailjet\Services\ContactMetadataService;
 use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\LaravelMailjet\Services\ContactMetadataService;
+use Mailjet\LaravelMailjet\Contracts\ContactMetadataContract;
 
 class ContactMetadataServiceProvider extends ServiceProvider
 {
+    /**
+     * Indicates if loading of the provider is deferred.
+     *
+     * @var bool
+     */
     protected $defer = true;
 
     /**
@@ -15,9 +23,8 @@ class ContactMetadataServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
-
     }
 
     /**
@@ -25,14 +32,15 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        $this->app->bind('Mailjet\LaravelMailjet\Contracts\ContactMetadataContract',
-            function($app) {
-            $config  = $this->app['config']->get('services.mailjet', array());
-            $call    = $this->app['config']->get('services.mailjet.common.call',true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
-            $mailjetService=new MailjetService($config['key'], $config['secret'], $call,$options);
+        $this->app->bind(ContactMetadataContract::class, function () {
+            $config = $this->app['config']->get('services.mailjet', []);
+            $call = $this->app['config']->get('services.mailjet.common.call', true);
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
+
+            $mailjetService = new MailjetService($config['key'], $config['secret'], $call, $options);
+
             return new ContactMetadataService($mailjetService);
         });
     }
@@ -42,8 +50,8 @@ function($app) {
      *
      * @return array
      */
-    public function provides()
+    public function provides(): array
     {
-        return ['Mailjet\LaravelMailjet\Contracts\ContactMetadataContract'];
+        return [ContactMetadataContract::class];
     }
-}
\ No newline at end of file
+}
diff --git a/src/Providers/ContactsListServiceProvider.php b/src/Providers/ContactsListServiceProvider.php
index 9a08f84..14a8917 100644
--- a/src/Providers/ContactsListServiceProvider.php
+++ b/src/Providers/ContactsListServiceProvider.php
@@ -1,13 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Providers;
 
 use Illuminate\Support\ServiceProvider;
-use Mailjet\LaravelMailjet\Services\ContactsListService;
 use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\LaravelMailjet\Services\ContactsListService;
+use Mailjet\LaravelMailjet\Contracts\ContactsListContract;
 
 class ContactsListServiceProvider extends ServiceProvider
 {
+    /**
+     * Indicates if loading of the provider is deferred.
+     *
+     * @var bool
+     */
     protected $defer = true;
 
     /**
@@ -15,9 +23,8 @@ class ContactsListServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
-
     }
 
     /**
@@ -25,14 +32,15 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        $this->app->bind('Mailjet\LaravelMailjet\Contracts\ContactsListContract',
-            function($app) {
-            $config  = $this->app['config']->get('services.mailjet', array());
-            $call    = $this->app['config']->get('services.mailjet.common.call',true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
-            $mailjetService=new MailjetService($config['key'], $config['secret'], $call,$options);
+        $this->app->bind(ContactsListContract::class, function () {
+            $config = $this->app['config']->get('services.mailjet', []);
+            $call = $this->app['config']->get('services.mailjet.common.call', true);
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
+
+            $mailjetService = new MailjetService($config['key'], $config['secret'], $call, $options);
+
             return new ContactsListService($mailjetService);
         });
     }
@@ -42,8 +50,8 @@ function($app) {
      *
      * @return array
      */
-    public function provides()
+    public function provides(): array
     {
-        return ['Mailjet\LaravelMailjet\Contracts\ContactsListContract'];
+        return [ContactsListContract::class];
     }
-}
\ No newline at end of file
+}
diff --git a/src/Providers/EventCallbackUrlServiceProvider.php b/src/Providers/EventCallbackUrlServiceProvider.php
index ab689ec..a7f6d67 100644
--- a/src/Providers/EventCallbackUrlServiceProvider.php
+++ b/src/Providers/EventCallbackUrlServiceProvider.php
@@ -1,13 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Providers;
 
 use Illuminate\Support\ServiceProvider;
-use Mailjet\LaravelMailjet\Services\EventCallbackUrlService;
 use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\LaravelMailjet\Services\EventCallbackUrlService;
+use Mailjet\LaravelMailjet\Contracts\EventCallbackUrlContract;
 
 class EventCallbackUrlServiceProvider extends ServiceProvider
 {
+    /**
+     * Indicates if loading of the provider is deferred.
+     *
+     * @var bool
+     */
     protected $defer = true;
 
     /**
@@ -15,9 +23,8 @@ class EventCallbackUrlServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
-
     }
 
     /**
@@ -25,14 +32,15 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        $this->app->bind('Mailjet\LaravelMailjet\Contracts\EventCallbackUrlContract',
-            function($app) {
-            $config  = $this->app['config']->get('services.mailjet', array());
-            $call    = $this->app['config']->get('services.mailjet.common.call',true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
-            $mailjetService=new MailjetService($config['key'], $config['secret'], $call,$options);
+        $this->app->bind(EventCallbackUrlContract::class, function () {
+            $config = $this->app['config']->get('services.mailjet', []);
+            $call = $this->app['config']->get('services.mailjet.common.call', true);
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
+
+            $mailjetService = new MailjetService($config['key'], $config['secret'], $call, $options);
+
             return new EventCallbackUrlService($mailjetService);
         });
     }
@@ -42,8 +50,8 @@ function($app) {
      *
      * @return array
      */
-    public function provides()
+    public function provides(): array
     {
-        return ['Mailjet\LaravelMailjet\Contracts\EventCallbackUrlContract'];
+        return [EventCallbackUrlContract::class];
     }
-}
\ No newline at end of file
+}
diff --git a/src/Providers/MailjetClientServiceProvider.php b/src/Providers/MailjetClientServiceProvider.php
index 0049a8a..e7eb098 100644
--- a/src/Providers/MailjetClientServiceProvider.php
+++ b/src/Providers/MailjetClientServiceProvider.php
@@ -1,19 +1,28 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Providers;
 
 use Illuminate\Support\ServiceProvider;
 use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\LaravelMailjet\Contracts\MailjetServiceContract;
 
 class MailjetClientServiceProvider extends ServiceProvider
 {
+    /**
+     * Indicates if loading of the provider is deferred.
+     *
+     * @var bool
+     */
     protected $defer = true;
+
     /**
      * Bootstrap the application services.
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
     }
 
@@ -22,21 +31,24 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        
-         $this->app->bind('Mailjet\LaravelMailjet\Contracts\MailjetServiceContract', function ($app) {
-            $config = $this->app['config']->get('services.mailjet', array());
+        $this->app->bind(MailjetServiceContract::class, function () {
+            $config = $this->app['config']->get('services.mailjet', []);
             $call = $this->app['config']->get('services.mailjet.common.call', true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
 
             return new MailjetService($config['key'], $config['secret'], $call, $options);
         });
     }
 
-
-    public function provides()
+    /**
+     * Get the services provided by the provider.
+     *
+     * @return array
+     */
+    public function provides(): array
     {
-        return ['Mailjet\LaravelMailjet\Contracts\MailjetServiceContract'];
+        return [MailjetServiceContract::class];
     }
 }
diff --git a/src/Providers/TemplateServiceProvider.php b/src/Providers/TemplateServiceProvider.php
index fbd464c..8080536 100644
--- a/src/Providers/TemplateServiceProvider.php
+++ b/src/Providers/TemplateServiceProvider.php
@@ -1,13 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Providers;
 
 use Illuminate\Support\ServiceProvider;
-use Mailjet\LaravelMailjet\Services\TemplateService;
 use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\LaravelMailjet\Services\TemplateService;
+use Mailjet\LaravelMailjet\Contracts\TemplateServiceContract;
 
 class TemplateServiceProvider extends ServiceProvider
 {
+    /**
+     * Indicates if loading of the provider is deferred.
+     *
+     * @var bool
+     */
     protected $defer = true;
 
     /**
@@ -15,9 +23,8 @@ class TemplateServiceProvider extends ServiceProvider
      *
      * @return void
      */
-    public function boot()
+    public function boot(): void
     {
-
     }
 
     /**
@@ -25,14 +32,15 @@ public function boot()
      *
      * @return void
      */
-    public function register()
+    public function register(): void
     {
-        $this->app->bind('Mailjet\LaravelMailjet\Contracts\TemplateServiceContract',
-            function($app) {
-            $config  = $this->app['config']->get('services.mailjet', array());
-            $call    = $this->app['config']->get('services.mailjet.common.call',true);
-            $options = $this->app['config']->get('services.mailjet.common.options', array());
-            $mailjetService=new MailjetService($config['key'], $config['secret'], $call,$options);
+        $this->app->bind(TemplateServiceContract::class, function () {
+            $config = $this->app['config']->get('services.mailjet', []);
+            $call = $this->app['config']->get('services.mailjet.common.call', true);
+            $options = $this->app['config']->get('services.mailjet.common.options', []);
+
+            $mailjetService = new MailjetService($config['key'], $config['secret'], $call, $options);
+
             return new TemplateService($mailjetService);
         });
     }
@@ -42,8 +50,8 @@ function($app) {
      *
      * @return array
      */
-    public function provides()
+    public function provides(): array
     {
-        return ['Mailjet\LaravelMailjet\Contracts\TemplateServiceContract'];
+        return [TemplateServiceContract::class];
     }
-}
\ No newline at end of file
+}
diff --git a/src/Services/CampaignDraftService.php b/src/Services/CampaignDraftService.php
index 21d9eb9..bfa613d 100644
--- a/src/Services/CampaignDraftService.php
+++ b/src/Services/CampaignDraftService.php
@@ -1,23 +1,22 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Services;
 
-use \Mailjet\Resources;
-use \Mailjet\Response;
-use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\Response;
+use Mailjet\Resources;
 use Mailjet\LaravelMailjet\Model\CampaignDraft;
-use Mailjet\LaravelMailjet\Contracts\CampaignDraftContract;
 use Mailjet\LaravelMailjet\Exception\MailjetException;
+use Mailjet\LaravelMailjet\Contracts\CampaignDraftContract;
 
 /**
  * https://dev.mailjet.com/email-api/v3/campaigndraft/
- * CampaignDraft data. (list,view, create, update, delete,schedule,send ...)
  */
 class CampaignDraftService implements CampaignDraftContract
 {
     /**
-     * Mailjet client
-     * @var MailjetClient
+     * @var MailjetService
      */
     protected $mailjet;
 
@@ -27,32 +26,35 @@ public function __construct(MailjetService $mailjet)
     }
 
     /**
-     * List campaigndraft resources available for this apikey
+     * List campaign draft resources available for this apikey.
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getAllCampaignDrafts(array $filters = null)
+    public function getAllCampaignDrafts(array $filters = null): array
     {
-        $response = $this->mailjet->get(Resources::$Campaigndraft,
-            ['filters' => $filters]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService :getAllCampaignDrafts() failed",
-                $response);
+        $response = $this->mailjet->get(Resources::$Campaigndraft, ['filters' => $filters]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'CampaignDraftService :getAllCampaignDrafts() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Access a given campaigndraft resource
-     * @param string $CampaignId
+     * Access a given CampaignDraft resource.
+     *
+     * @param string $id
+     *
      * @return array
      */
-    public function findByCampaignDraftId($CampaignId)
+    public function findByCampaignDraftId(string $id)
     {
         $response = $this->mailjet->get(Resources::$Campaigndraft,
-            ['id' => $CampaignId]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:findByCampaignDraftId() failed",
+            ['id' => $id]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:findByCampaignDraftId() failed',
                 $response);
         }
 
@@ -61,14 +63,15 @@ public function findByCampaignDraftId($CampaignId)
 
     /**
      * create a new fresh CampaignDraft
+     *
      * @param Campaigndraft $campaignDraft
      */
     public function create(CampaignDraft $campaignDraft)
     {
         $response = $this->mailjet->post(Resources::$Campaigndraft,
             ['body' => $campaignDraft->format()]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:create() failed", $response);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:create() failed', $response);
         }
 
         return $response->getData();
@@ -76,15 +79,16 @@ public function create(CampaignDraft $campaignDraft)
 
     /**
      * Update one specific campaigndraft resource
-     * @param int $id
+     *
+     * @param int           $id
      * @param Campaigndraft $campaignDraft
      */
-    public function update($CampaignId, CampaignDraft $campaignDraft)
+    public function update($id, CampaignDraft $campaignDraft)
     {
         $response = $this->mailjet->put(Resources::$Campaigndraft,
-            ['id' => $CampaignId, 'body' => $campaignDraft->format()]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:update() failed", $response);
+            ['id' => $id, 'body' => $campaignDraft->format()]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:update() failed', $response);
         }
 
         return $response->getData();
@@ -92,15 +96,17 @@ public function update($CampaignId, CampaignDraft $campaignDraft)
 
     /**
      * Return the text and html contents of the campaigndraft
+     *
      * @param string $id
+     *
      * @return array
      */
-    public function getDetailContent($id)
+    public function getDetailContent(string $id)
     {
         $response = $this->mailjet->get(Resources::$CampaigndraftDetailcontent,
             ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:getDetailContent failed",
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:getDetailContent failed',
                 $response);
         }
 
@@ -109,15 +115,17 @@ public function getDetailContent($id)
 
     /**
      * Creates the content of a  campaigndraft
+     *
      * @param string $id
+     *
      * @return array
      */
     public function createDetailContent($id, $contentData)
     {
         $response = $this->mailjet->post(Resources::$CampaigndraftDetailcontent,
             ['id' => $id, 'body' => $contentData]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:createDetailContent failed",
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:createDetailContent failed',
                 $response);
         }
 
@@ -126,15 +134,17 @@ public function createDetailContent($id, $contentData)
 
     /**
      * Return the date of the scheduled sending of the campaigndraft
+     *
      * @param string Campaign $id
+     *
      * @return array
      */
-    public function getSchedule($CampaignId)
+    public function getSchedule(string $id)
     {
         $response = $this->mailjet->get(Resources::$CampaigndraftSchedule,
-            ['id' => $CampaignId]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:getSchedule failed",
+            ['id' => $id]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:getSchedule failed',
                 $response);
         }
 
@@ -143,16 +153,18 @@ public function getSchedule($CampaignId)
 
     /**
      * Schedule when the campaigndraft will be sent
-     * @param string Campaign $id
-     * @param RFC3339 format "Y-m-d\TH:i:sP"  $date
+     *
+     * @param string $id
+     * @param string $date (RFC3339 format "Y-m-d\TH:i:sP")
+     *
      * @return array
      */
-    public function scheduleCampaign($CampaignId, $date)
+    public function scheduleCampaign(string $id, string $date)
     {
         $response = $this->mailjet->post(Resources::$CampaigndraftSchedule,
-            ['id' => $CampaignId, 'body' => $date]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:scheduleCampaign failed",
+            ['id' => $id, 'body' => $date]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:scheduleCampaign failed',
                 $response);
         }
 
@@ -161,16 +173,18 @@ public function scheduleCampaign($CampaignId, $date)
 
     /**
      * Update the date when the campaigndraft will be sent
+     *
      * @param string Campaign $id
      * @param string Schedule $date
+     *
      * @return array
      */
-    public function updateCampaignSchedule($CampaignId, $date)
+    public function updateCampaignSchedule($id, $date)
     {
         $response = $this->mailjet->put(Resources::$CampaigndraftSchedule,
-            ['id' => $CampaignId, 'body' => $date]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:updateCampaignSchedule failed",
+            ['id' => $id, 'body' => $date]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:updateCampaignSchedule failed',
                 $response);
         }
 
@@ -179,15 +193,17 @@ public function updateCampaignSchedule($CampaignId, $date)
 
     /**
      * Cancel a future sending
+     *
      * @param string Campaign $id
+     *
      * @return array
      */
-    public function removeSchedule($CampaignId)
+    public function removeSchedule(string $id)
     {
         $response = $this->mailjet->delete(Resources::$CampaigndraftSchedule,
-            ['id' => $CampaignId]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:removeSchedule failed",
+            ['id' => $id]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:removeSchedule failed',
                 $response);
         }
 
@@ -196,15 +212,17 @@ public function removeSchedule($CampaignId)
 
     /**
      * Send the campaign immediately
+     *
      * @param string Campaign $id
+     *
      * @return array
      */
-    public function sendCampaign($CampaignId)
+    public function sendCampaign(string $id)
     {
         $response = $this->mailjet->post(Resources::$CampaigndraftSend,
-            ['id' => $CampaignId]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:sendCampaign failed",
+            ['id' => $id]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:sendCampaign failed',
                 $response);
         }
 
@@ -213,15 +231,17 @@ public function sendCampaign($CampaignId)
 
     /**
      * Return the status of a CampaignDraft
+     *
      * @param string Campaign $id
+     *
      * @return array
      */
-    public function getCampaignStatus($CampaignId)
+    public function getCampaignStatus(string $id)
     {
         $response = $this->mailjet->get(Resources::$CampaigndraftStatus,
-            ['id' => $CampaignId]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:getCampaignStatus failed",
+            ['id' => $id]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:getCampaignStatus failed',
                 $response);
         }
 
@@ -230,16 +250,18 @@ public function getCampaignStatus($CampaignId)
 
     /**
      * An action to test a CampaignDraft.
+     *
      * @param string Campaign $id
      * @param array of  $recipients
+     *
      * @return array
      */
-    public function testCampaign($CampaignId, $recipients)
+    public function testCampaign($id, $recipients)
     {
         $response = $this->mailjet->post(Resources::$CampaigndraftTest,
-            ['id' => $CampaignId, 'body' => $recipients]);
-        if (!$response->success()) {
-            $this->throwError("CampaignDraftService:testCampaign failed",
+            ['id' => $id, 'body' => $recipients]);
+        if (! $response->success()) {
+            $this->throwError('CampaignDraftService:testCampaign failed',
                 $response);
         }
 
@@ -250,4 +272,4 @@ private function throwError($title, Response $response)
     {
         throw new MailjetException(0, $title, $response);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Services/CampaignService.php b/src/Services/CampaignService.php
index d41a72c..c246b3c 100644
--- a/src/Services/CampaignService.php
+++ b/src/Services/CampaignService.php
@@ -1,87 +1,100 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Services;
 
-use \Mailjet\Resources;
-use \Mailjet\Response;
-use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\Resources;
 use Mailjet\LaravelMailjet\Model\Campaign;
 use Mailjet\LaravelMailjet\Contracts\CampaignContract;
 use Mailjet\LaravelMailjet\Exception\MailjetException;
 
 /**
  * https://dev.mailjet.com/email-api/v3/campaign/
- * list/view/update
  */
-class CampaignService implements CampaignContract {
-
+class CampaignService implements CampaignContract
+{
     /**
-     * Mailjet client
-     * @var MailjetClient
+     * @var MailjetService
      */
     protected $mailjet;
 
-    public function __construct(MailjetService $mailjet) {
+    public function __construct(MailjetService $mailjet)
+    {
         $this->mailjet = $mailjet;
     }
 
     /**
      * List campaigns resources available for this apikey
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getAllCampaigns(array $filters = null) {
+    public function getAllCampaigns(array $filters = null): array
+    {
         $response = $this->mailjet->get(Resources::$Campaign, ['filters' => $filters]);
-        if (!$response->success()) {
-            $this->throwError("CampaignService:getAllCampaigns() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'CampaignService:getAllCampaigns() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Access a given campaign resource
-     * @param string $CampaignId
+     * Access a given campaign resource.
+     *
+     * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function findByCampaignId($CampaignId) {
-        $response = $this->mailjet->get(Resources::$Campaign, ['id' => $CampaignId]);
-        if (!$response->success()) {
-            $this->throwError("CampaignService:findByCampaignId() failed", $response);
+    public function findByCampaignId(string $id): array
+    {
+        $response = $this->mailjet->get(Resources::$Campaign, ['id' => $id]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'CampaignService:findByCampaignId() failed', $response);
         }
 
         return $response->getData();
     }
 
-     /**
-     * Find a given campaign by Newsletter/campaigndraftId
-     * @param string $NewsletterId
+    /**
+     * Find a given campaign by Newsletter / CampaignDraft id.
+     *
+     * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function findByNewsletterId($NewsletterId) {
-        $response = $this->mailjet->get(Resources::$Campaign, ['mj.nl' => $NewsletterId]);
-        if (!$response->success()) {
-            $this->throwError("CampaignService:findByNewsletterId() failed", $response);
+    public function findByNewsletterId(string $id): array
+    {
+        $response = $this->mailjet->get(Resources::$Campaign, ['mj.nl' => $id]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'CampaignService:findByNewsletterId() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Update one specific campaign resource with a PUT request, providing the campaign's ID value
+     * Update one specific campaign resource with a PUT request.
+     *
      * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function updateCampaign($CampaignId, Campaign $campaign) {
-        $response = $this->mailjet->put(Resources::$Campaign, ['id' => $CampaignId, 'body' => $campaign->format()]);
-        if (!$response->success()) {
-            $this->throwError("CampaignService:updateCampaign() failed", $response);
+    public function updateCampaign(string $id, Campaign $campaign): array
+    {
+        $response = $this->mailjet->put(Resources::$Campaign, ['id' => $id, 'body' => $campaign->format()]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'CampaignService:updateCampaign() failed', $response);
         }
 
         return $response->getData();
     }
-
-    private function throwError($title, Response $response) {
-        throw new MailjetException(0, $title, $response);
-    }
-
 }
diff --git a/src/Services/ContactMetadataService.php b/src/Services/ContactMetadataService.php
index 6fa5403..42415c3 100644
--- a/src/Services/ContactMetadataService.php
+++ b/src/Services/ContactMetadataService.php
@@ -1,59 +1,60 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Services;
 
-use \Mailjet\Resources;
-use \Mailjet\Response;
-use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\Resources;
 use Mailjet\LaravelMailjet\Model\ContactMetadata;
-use Mailjet\LaravelMailjet\Contracts\ContactMetadataContract;
 use Mailjet\LaravelMailjet\Exception\MailjetException;
+use Mailjet\LaravelMailjet\Contracts\ContactMetadataContract;
 
 /**
-* https://dev.mailjet.com/email-api/v3/contactmetadata/
-* manage ContactsMetadata (create, update, delete, ...)
-*
-*/
+ * https://dev.mailjet.com/email-api/v3/contactmetadata/
+ */
 class ContactMetadataService implements ContactMetadataContract
 {
     /**
-     * Mailjet client
-     * @var MailjetClient
+     * @var MailjetService
      */
     protected $mailjet;
 
-    /**
-     * @param MailjetClient $mailjet
-     */
     public function __construct(MailjetService $mailjet)
     {
         $this->mailjet = $mailjet;
     }
 
     /**
-     * Retrieve all ContactMetadata
+     * Retrieve all ContactMetadata.
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getAll()
+    public function getAll(): array
     {
         $response = $this->mailjet->get(Resources::$Contactmetadata);
-        if (!$response->success()) {
-            $this->throwError("ContactMetadataService:getAll() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactMetadataService:getAll() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Retrieve one ContactMetadata
+     * Retrieve one ContactMetadata.
+     *
      * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function get($id)
+    public function get(string $id): array
     {
         $response = $this->mailjet->get(Resources::$Contactmetadata, ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("ContactMetadataService:get() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactMetadataService:get() failed', $response);
         }
 
         return $response->getData();
@@ -61,13 +62,17 @@ public function get($id)
 
     /**
      * create a new fresh ContactMetadata
-     * @param ContactMetadata $contactMetadata
+     *
+     * @param ContactMetadata $metadata
+     *
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function create(ContactMetadata $contactMetadata)
+    public function create(ContactMetadata $metadata): array
     {
-        $response = $this->mailjet->post(Resources::$Contactmetadata, ['body' => $contactMetadata->format()]);
-        if (!$response->success()) {
-            $this->throwError("ContactMetadataService:create() failed", $response);
+        $response = $this->mailjet->post(Resources::$Contactmetadata, ['body' => $metadata->format()]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactMetadataService:create() failed', $response);
         }
 
         return $response->getData();
@@ -75,14 +80,18 @@ public function create(ContactMetadata $contactMetadata)
 
     /**
      * Update one ContactMetadata
-     * @param int $id
-     * @param ContactMetadata $contactMetadata
+     *
+     * @param string          $id
+     * @param ContactMetadata $metadata
+     *
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function update($id, ContactMetadata $contactMetadata)
+    public function update(string $id, ContactMetadata $metadata): array
     {
-        $response = $this->mailjet->put(Resources::$Contactmetadata, ['id' => $id,'body' => $contactMetadata->format()]);
-        if (!$response->success()) {
-            $this->throwError("ContactMetadataService:update() failed", $response);
+        $response = $this->mailjet->put(Resources::$Contactmetadata, ['id' => $id, 'body' => $metadata->format()]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactMetadataService:update() failed', $response);
         }
 
         return $response->getData();
@@ -90,25 +99,19 @@ public function update($id, ContactMetadata $contactMetadata)
 
     /**
      * Delete one ContactMetadata
-     * @param int $id
+     *
+     * @param string $id
+     *
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function delete($id)
+    public function delete(string $id): array
     {
         $response = $this->mailjet->delete(Resources::$Contactmetadata, ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("ContactMetadataService:delete() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactMetadataService:delete() failed', $response);
         }
 
         return $response->getData();
     }
-
-    /**
-     * Helper to throw error
-     * @param  string $title
-     * @param  Response $response
-     */
-    private function throwError($title, Response $response)
-    {
-        throw new MailjetException(0, $title, $response);
-    }
 }
diff --git a/src/Services/ContactsListService.php b/src/Services/ContactsListService.php
index 5b5b748..f101297 100644
--- a/src/Services/ContactsListService.php
+++ b/src/Services/ContactsListService.php
@@ -1,107 +1,122 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Services;
 
-use \Mailjet\Resources;
-use \Mailjet\Response;
-use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\Response;
+use Mailjet\Resources;
 use Mailjet\LaravelMailjet\Model\Contact;
 use Mailjet\LaravelMailjet\Model\ContactsList;
-use Mailjet\LaravelMailjet\Contracts\ContactsListContract;
 use Mailjet\LaravelMailjet\Exception\MailjetException;
+use Mailjet\LaravelMailjet\Contracts\ContactsListContract;
 
 /**
-* https://dev.mailjet.com/email-api/v3/contactslist-managecontact/
-* manage ContactsList (create, update, delete, ...)
-*
-*/
+ * https://dev.mailjet.com/email-api/v3/contactslist-managecontact/
+ */
 class ContactsListService implements ContactsListContract
 {
     /**
      * @var int
      */
-    const CONTACT_BATCH_SIZE = 1000;
+    public const CONTACT_BATCH_SIZE = 1000;
 
     /**
-     * Mailjet client
-     * @var MailjetClient
+     * @var MailjetService
      */
     protected $mailjet;
 
-    /**
-     * @param MailjetClient $mailjet
-     */
     public function __construct(MailjetService $mailjet)
     {
         $this->mailjet = $mailjet;
     }
 
     /**
-     * create a new fresh Contact to listId
-     * @param string $listId
+     * Create a new fresh Contact to listId.
+     *
+     * @param string  $id
      * @param Contact $contact
-     * @param string $action
+     * @param string  $action
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function create($listId, Contact $contact, $action=Contact::ACTION_ADDFORCE)
+    public function create(string $id, Contact $contact, $action = Contact::ACTION_ADDFORCE): array
     {
         $contact->setAction($action);
-        $response = $this->_exec($listId, $contact);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:create() failed", $response);
+
+        $response = $this->_exec($id, $contact);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:create() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * update a Contact to listId
-     * @param string $listId
+     * Update a Contact to listId.
+     *
+     * @param string  $id
      * @param Contact $contact
-     * @param string $action
+     * @param string  $action
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function update($listId, Contact $contact, $action=Contact::ACTION_ADDNOFORCE)
+    public function update(string $id, Contact $contact, $action = Contact::ACTION_ADDNOFORCE): array
     {
         $contact->setAction($action);
-        $response = $this->_exec($listId, $contact);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:update() failed", $response);
+
+        $response = $this->_exec($id, $contact);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:update() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * re/subscribe a Contact to listId
-     * @param string $listId
+     * Re/subscribe a Contact to listId.
+     *
+     * @param string  $id
      * @param Contact $contact
-     * @param bool $force
+     * @param bool    $force
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function subscribe($listId, Contact $contact, $force = true)
+    public function subscribe(string $id, Contact $contact, bool $force = true): array
     {
-        if ($force) {
-            $contact->setAction(Contact::ACTION_ADDFORCE);
-        } else {
-            $contact->setAction(Contact::ACTION_ADDNOFORCE);
-        }
-        $response = $this->_exec($listId, $contact);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:subscribe() failed", $response);
+        $contact->setAction($force ? Contact::ACTION_ADDFORCE : Contact::ACTION_ADDNOFORCE);
+
+        $response = $this->_exec($id, $contact);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:subscribe() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * unsubscribe a Contact from listId
-     * @param string $listId
+     * Unsubscribe a Contact from listId.
+     *
+     * @param string  $id
      * @param Contact $contact
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function unsubscribe($listId, Contact $contact)
+    public function unsubscribe(string $id, Contact $contact): array
     {
         $contact->setAction(Contact::ACTION_UNSUB);
-        $response = $this->_exec($listId, $contact);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:unsubscribe() failed", $response);
+
+        $response = $this->_exec($id, $contact);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:unsubscribe() failed', $response);
         }
 
         return $response->getData();
@@ -109,111 +124,118 @@ public function unsubscribe($listId, Contact $contact)
 
     /**
      * Delete a Contact from listId
-     * @param string $listId
+     *
+     * @param string  $id
      * @param Contact $contact
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function delete($listId, Contact $contact)
+    public function delete(string $id, Contact $contact): array
     {
         $contact->setAction(Contact::ACTION_REMOVE);
-        $response = $this->_exec($listId, $contact);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:delete() failed", $response);
+
+        $response = $this->_exec($id, $contact);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:delete() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Change email a Contact
-     * @param string $listId
+     * Change email a Contact.
+     *
+     * @param string  $id
      * @param Contact $contact
-     * @param string $oldEmail
+     * @param string  $oldEmail
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function updateEmail($listId, Contact $contact, $oldEmail)
+    public function updateEmail(string $id, Contact $contact, string $oldEmail): array
     {
-        // get old contact properties
         $response = $this->mailjet->get(Resources::$Contactdata, ['id' => $oldEmail]);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:changeEmail() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:changeEmail() failed', $response);
         }
 
-        // copy contact properties
         $oldContactData = $response->getData();
+
         if (isset($oldContactData[0])) {
             $contact->setProperties($oldContactData[0]['Data']);
         }
 
-        // add new contact
         $contact->setAction(Contact::ACTION_ADDFORCE);
-        $response = $this->_exec($listId, $contact);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:changeEmail() failed", $response);
+        $response = $this->_exec($id, $contact);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:changeEmail() failed', $response);
         }
 
-        // remove old
         $oldContact = new Contact($oldEmail);
         $oldContact->setAction(Contact::ACTION_REMOVE);
-        $response = $this->_exec($listId, $oldContact);
-        if (!$response->success()) {
-            $this->throwError("ContactsListService:changeEmail() failed", $response);
+        $response = $this->_exec($id, $oldContact);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'ContactsListService:changeEmail() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Import many contacts to a list
+     * Import many contacts to a list.
      * https://dev.mailjet.com/email-api/v3/contactslist-managemanycontacts/
-     * @param  ContactsList $contactsList
+     *
+     * @param ContactsList $list
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function uploadManyContactsList(ContactsList $contactsList)
+    public function uploadManyContactsList(ContactsList $list): array
     {
         $batchResults = [];
-        // we send multiple smaller requests instead of a bigger one
-        $contactChunks = array_chunk($contactsList->getContacts(), self::CONTACT_BATCH_SIZE);
+        $contactChunks = array_chunk($list->getContacts(), self::CONTACT_BATCH_SIZE);
+
         foreach ($contactChunks as $contactChunk) {
-            // create a sub-contactList to divide large request
-            $subContactsList = new ContactsList($contactsList->getListId(), $contactsList->getAction(), $contactChunk);
+            $subContactsList = new ContactsList($list->getListId(), $list->getAction(), $contactChunk);
             $currentBatch = $this->mailjet->post(Resources::$ContactslistManagemanycontacts,
                 ['id' => $subContactsList->getListId(), 'body' => $subContactsList->format()]
             );
+
             if ($currentBatch->success()) {
-                array_push($batchResults, $currentBatch->getData()[0]);
+                $batchResults[] = $currentBatch->getData()[0];
             } else {
-                $this->throwError("ContactsListService:manageManyContactsList() failed", $currentBatch);
+                throw new MailjetException(0, 'ContactsListService:manageManyContactsList() failed', $currentBatch);
             }
         }
+
         return $batchResults;
     }
 
     /**
-    * An action for adding a contact to a contact list. Only POST is supported.
-    * The API will internally create the new contact if it does not exist,
-    * add or update the name and properties.
-    * The properties have to be defined before they can be used.
-    * The API then adds the contact to the contact list with active=true and
-    * unsub=specified value if it is not already in the list,
-    * or updates the entry with these values. On success,
-    * the API returns a packet with the same format but with all properties available
-    * for that contact.
-    * @param string $listId
-    * @param Contact $contact
-    */
-    private function _exec($listId, Contact $contact)
+     * An action for adding a contact to a contact list. Only POST is supported.
+     * The API will internally create the new contact if it does not exist,
+     * add or update the name and properties.
+     * The properties have to be defined before they can be used.
+     * The API then adds the contact to the contact list with active=true
+     * and unsub=specified value if it is not already in the list,
+     * or updates the entry with these values.
+     * On success, the API returns a packet with the same format
+     * but with all properties available for that contact.
+     *
+     * @param string  $id
+     * @param Contact $contact
+     *
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
+     */
+    private function _exec(string $id, Contact $contact): Response
     {
         return $this->mailjet->post(Resources::$ContactslistManagecontact,
-            ['id' => $listId, 'body' => $contact->format()]
+            ['id' => $id, 'body' => $contact->format()]
         );
     }
-
-    /**
-     * Helper to throw error
-     * @param  string $title
-     * @param  Response $response
-     */
-     private function throwError($title, Response $response)
-     {
-         throw new MailjetException(0, $title, $response);
-     }
 }
diff --git a/src/Services/EventCallbackUrlService.php b/src/Services/EventCallbackUrlService.php
index 8859ed5..b03c76b 100644
--- a/src/Services/EventCallbackUrlService.php
+++ b/src/Services/EventCallbackUrlService.php
@@ -1,118 +1,120 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Services;
 
-use \Mailjet\Resources;
-use \Mailjet\Response;
-use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\Resources;
 use Mailjet\LaravelMailjet\Model\EventCallbackUrl;
-use Mailjet\LaravelMailjet\Contracts\EventCallbackUrlContract;
 use Mailjet\LaravelMailjet\Exception\MailjetException;
+use Mailjet\LaravelMailjet\Contracts\EventCallbackUrlContract;
 
 /**
-* https://dev.mailjet.com/email-api/v3/eventcallbackurl/
-* Manage EventCallbackUrl
-*/
+ * https://dev.mailjet.com/email-api/v3/eventcallbackurl/
+ */
 class EventCallbackUrlService implements EventCallbackUrlContract
 {
-
     /**
-     * Mailjet client
-     * @var MailjetClient
+     * @var MailjetService
      */
     protected $mailjet;
-
-    /**
-     * @param MailjetClient $mailjet
-     */
+    
     public function __construct(MailjetService $mailjet)
     {
         $this->mailjet = $mailjet;
     }
 
     /**
-     * Retrieve all EventCallbackUrl
+     * Retrieve all EventCallbackUrl.
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getAll()
+    public function getAll(): array
     {
         $response = $this->mailjet->get(Resources::$Eventcallbackurl);
-        if (!$response->success()) {
-            $this->throwError("EventCallbackUrlService:getAll() failed", $response);
+        
+        if (! $response->success()) {
+            throw new MailjetException(0, 'EventCallbackUrlService:getAll() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Retrieve one EventCallbackUrl
+     * Retrieve one EventCallbackUrl.
+     *
      * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function get($id)
+    public function get(string $id): array
     {
         $response = $this->mailjet->get(Resources::$Eventcallbackurl, ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("EventCallbackUrlService:get() failed", $response);
+        
+        if (! $response->success()) {
+            throw new MailjetException(0, 'EventCallbackUrlService:get() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Create one EventCallbackUrl
-     * @param EventCallbackUrl $eventCallbackUrl
+     * Create one EventCallbackUrl.
+     *
+     * @param EventCallbackUrl $url
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function create(EventCallbackUrl $eventCallbackUrl)
+    public function create(EventCallbackUrl $url): array
     {
-        $response = $this->mailjet->post(Resources::$Eventcallbackurl, ['body' => $eventCallbackUrl->format()]);
-        if (!$response->success()) {
-            $this->throwError("EventCallbackUrlService:create() failed", $response);
+        $response = $this->mailjet->post(Resources::$Eventcallbackurl, ['body' => $url->format()]);
+        
+        if (! $response->success()) {
+            throw new MailjetException(0, 'EventCallbackUrlService:create() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Update one EventCallbackUrl
-     * @param string $id
-     * @param EventCallbackUrl $eventCallbackUrl
+     * Update one EventCallbackUrl.
+     *
+     * @param string           $id
+     * @param EventCallbackUrl $url
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function update($id, EventCallbackUrl $eventCallbackUrl)
+    public function update(string $id, EventCallbackUrl $url): array
     {
-        $response = $this->mailjet->put(Resources::$Eventcallbackurl, ['id' => $id, 'body' => $eventCallbackUrl->format()]);
-        if (!$response->success()) {
-            $this->throwError("EventCallbackUrlService:update() failed", $response);
+        $response = $this->mailjet->put(Resources::$Eventcallbackurl, ['id' => $id, 'body' => $url->format()]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'EventCallbackUrlService:update() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Delete one EventCallbackUrl
+     * Delete one EventCallbackUrl.
+     *
      * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function delete($id)
+    public function delete(string $id): array
     {
         $response = $this->mailjet->delete(Resources::$Eventcallbackurl, ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("EventCallbackUrlService:delete() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'EventCallbackUrlService:delete() failed', $response);
         }
 
         return $response->getData();
     }
-
-    /**
-     * Helper to throw error
-     * @param  string $title
-     * @param  Response $response
-     * @param  array $response
-     */
-     private function throwError($title, Response $response)
-     {
-         throw new MailjetException(0, $title, $response);
-     }
-}
\ No newline at end of file
+}
diff --git a/src/Services/MailjetService.php b/src/Services/MailjetService.php
index 8634655..1420ebb 100644
--- a/src/Services/MailjetService.php
+++ b/src/Services/MailjetService.php
@@ -1,219 +1,253 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Services;
 
-use \Mailjet\Resources;
-use \Mailjet\Response;
-use \Mailjet\Client;
-use Mailjet\LaravelMailjet\Contracts\MailjetServiceContract;
+use Mailjet\Client;
+use Mailjet\Response;
+use Mailjet\Resources;
 use Mailjet\LaravelMailjet\Exception\MailjetException;
+use Mailjet\LaravelMailjet\Contracts\MailjetServiceContract;
 
 class MailjetService implements MailjetServiceContract
 {
     /**
-     * Mailjet Client
      * @var \Mailjet\Client
      */
     private $client;
 
-    /**
-     * Instanciate the client whit the api key and api secret given in the configuration
-     */
-    public function __construct($key, $secret, $call = true, array $settings = [])
+    public function __construct(string $key, string $secret, $call = true, array $settings = [])
     {
         $this->client = new Client($key, $secret, $call, $settings);
     }
 
     /**
-     * Trigger a POST request
+     * Trigger a POST request.
      *
      * @param array $resource Mailjet Resource/Action pair
      * @param array $args     Request arguments
      * @param array $options
      *
      * @return Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function post($resource, array $args = [], array $options = [])
+    public function post(array $resource, array $args = [], array $options = []): Response
     {
         $response = $this->client->post($resource, $args, $options);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:post() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:post() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * Trigger a GET request
+     * Trigger a GET request.
      *
      * @param array $resource Mailjet Resource/Action pair
      * @param array $args     Request arguments
      * @param array $options
      *
      * @return Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function get($resource, array $args = [], array $options = [])
+    public function get(array $resource, array $args = [], array $options = []): Response
     {
         $response = $this->client->get($resource, $args, $options);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:get() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:get() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * Trigger a PUT request
+     * Trigger a PUT request.
      *
      * @param array $resource Mailjet Resource/Action pair
      * @param array $args     Request arguments
      * @param array $options
      *
      * @return Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function put($resource, array $args = [], array $options = [])
+    public function put(array $resource, array $args = [], array $options = []): Response
     {
         $response = $this->client->put($resource, $args, $options);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:put() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:put() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * Trigger a DELETE request
+     * Trigger a DELETE request.
      *
      * @param array $resource Mailjet Resource/Action pair
      * @param array $args     Request arguments
      * @param array $options
      *
      * @return Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function delete($resource, array $args = [], array $options = [])
+    public function delete(array $resource, array $args = [], array $options = []): Response
     {
         $response = $this->client->delete($resource, $args, $options);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:delete() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:delete() failed', $response);
         }
+
         return $response;
     }
 
-
-
-    /**TODO exclude HIGH Level API methods into managers**/
     /**
-     * Get all list on your mailjet account
-     * @param  array $filters Filters that will be use to filter the request. See mailjet API documentation for all filters available
-     * @return array
+     * Get all list on your Mailjet account.
+     * TODO: Exclude HIGH Level API methods into managers.
+     *
+     * @param array $filters Filters that will be use to filter the request
+     *
+     * @return \Mailjet\Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getAllLists($filters)
+    public function getAllLists(array $filters = null): Response
     {
         $response = $this->client->get(Resources::$Contactslist, ['filters' => $filters]);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:getAllLists() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:getAllLists() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * Create a new list
-     * @param  array $body array containing the list informations. the 'Name' parameter is mandatory.See mailjet API documentation for all parameters available
-     * @return array
+     * Create a new list.
+     *
+     * @param array $body Information list - the 'Name' field is mandatory.
+     *
+     * @return \Mailjet\Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function createList($body)
+    public function createList(array $body): Response
     {
         $response = $this->client->post(Resources::$Contactslist, ['body' => $body]);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:createList() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:createList() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * Get all list recipient on your mailjet account
-     * @param  array $filters Filters that will be use to filter the request. See mailjet API documentation for all filters available
-     * @return array
+     * Get all list recipient on your Mailjet account.
+     *
+     * @param array $filters Filters that will be use to filter the request.
+     *
+     * @return \Mailjet\Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getListRecipients($filters)
+    public function getListRecipients(array $filters = null): Response
     {
         $response = $this->client->get(Resources::$Listrecipient, ['filters' => $filters]);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:getListRecipients() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:getListRecipients() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * Get single contact informations.
-     * @param  int $id ID of the contact
-     * @return array
+     * Get single contact information.
+     *
+     * @param string $id
+     *
+     * @return \Mailjet\Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getSingleContact($id)
+    public function getSingleContact(string $id): Response
     {
         $response = $this->client->get(Resources::$Contact, ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:getSingleContact() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:getSingleContact() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * create a contact
-     * @param  array $body array containing the list informations. the 'Email' parameter is mandatory.See mailjet API documentation for all parameters available
-     * @return array
+     * Create a contact.
+     *
+     * @param array $body Information list - the 'Email' field is mandatory.
+     *
+     * @return \Mailjet\Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function createContact($body)
+    public function createContact(array $body): Response
     {
         $response = $this->client->post(Resources::$Contact, ['body' => $body]);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:createContact() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:createContact() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * create a listrecipient (relationship between contact and list)
-     * @param  array $body array containing the list informations. the 'ContactID' and 'ListID' parameters are mandatory.See mailjet API documentation for all parameters available
-     * @return array
+     * Create a list recipient (relationship between contact and list).
+     *
+     * @param array $body Information list - the 'ContactID' and 'ListID' parameters are mandatory.
+     *
+     * @return \Mailjet\Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function createListRecipient($body)
+    public function createListRecipient(array $body): Response
     {
         $response = $this->client->post(Resources::$Listrecipient, ['body' => $body]);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:createListRecipient() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:createListRecipient() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * edit a list recipient
-     * @param  int $id   id of the list recipient
-     * @param  array $body array containing the list informations. the 'ContactID' and 'ListID' parameters are mandatory.See mailjet API documentation for all parameters available
-     * @return array
+     * Edit a list recipient.
+     *
+     * @param string $id
+     * @param array  $body Information list - the 'ContactID' and 'ListID' parameters are mandatory.
+     *
+     * @return \Mailjet\Response
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function editListrecipient($id, $body)
+    public function editListRecipient(string $id, array $body): Response
     {
-        $response = $this->client->put(Resources::$Listrecipient, ['id'=>$id, 'body' => $body]);
-        if (!$response->success()) {
-            $this->throwError("MailjetService:editListrecipient() failed", $response);
+        $response = $this->client->put(Resources::$Listrecipient, ['id' => $id, 'body' => $body]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'MailjetService:editListrecipient() failed', $response);
         }
+
         return $response;
     }
 
     /**
-     * Retrieve Mailjet\Client
-     * @return Client
+     * Retrieve Mailjet client.
+     *
+     * @return \Mailjet\Client
      */
-    public function getClient()
+    public function getClient(): Client
     {
         return $this->client;
     }
-
-    /**
-     * Helper to throw error
-     * @param  string $title
-     * @param  Response $response
-     */
-     private function throwError($title, Response $response)
-     {
-         throw new MailjetException(0, $title, $response);
-     }
 }
diff --git a/src/Services/TemplateService.php b/src/Services/TemplateService.php
index b44bc96..183142a 100644
--- a/src/Services/TemplateService.php
+++ b/src/Services/TemplateService.php
@@ -1,23 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Services;
 
-use \Mailjet\Resources;
-use \Mailjet\Response;
-use Mailjet\LaravelMailjet\Services\MailjetService;
+use Mailjet\Resources;
 use Mailjet\LaravelMailjet\Model\Template;
-use Mailjet\LaravelMailjet\Contracts\TemplateServiceContract;
 use Mailjet\LaravelMailjet\Exception\MailjetException;
+use Mailjet\LaravelMailjet\Contracts\TemplateServiceContract;
 
 /**
  * https://dev.mailjet.com/email-api/v3/template/
- * Template data. (list,view, create, update, delete,detailcontent, ...)
  */
 class TemplateService implements TemplateServiceContract
 {
     /**
-     * Mailjet client
-     * @var MailjetClient
+     * @var MailjetService
      */
     protected $mailjet;
 
@@ -29,30 +27,37 @@ public function __construct(MailjetService $mailjet)
     /**
      * List template resources available for this apikey, use a GET request.
      * Alternatively, you may want to add one or more filters.
-     * @param array optional $filters
-     * @return templates
+     *
+     * @param array|null $filters
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getAll(array $filters = null)
+    public function getAll(array $filters = null): array
     {
-        $response = $this->mailjet->get(Resources::$Template,
-            ['filters' => $filters]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService :getAll() failed", $response);
+        $response = $this->mailjet->get(Resources::$Template, ['filters' => $filters]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:getAll() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Access a given template resource, use a GET request, providing the template's ID value
+     * Access a given template resource, use a GET request, providing the template's ID value.
+     *
      * @param string $id
-     * @return $Template
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function get($id)
+    public function get(string $id): array
     {
         $response = $this->mailjet->get(Resources::$Template, ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService:get() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:get() failed', $response);
         }
 
         return $response->getData();
@@ -60,102 +65,117 @@ public function get($id)
 
     /**
      * Add a new template resource with a POST request.
-     * @param Template $Template
+     *
+     * @param Template $template
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function create(Template $Template)
+    public function create(Template $template): array
     {
-        $response = $this->mailjet->post(Resources::$Template,
-            ['body' => $Template->format()]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService:create() failed", $response);
+        $response = $this->mailjet->post(Resources::$Template, ['body' => $template->format()]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:create() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Update one specific template resource with a PUT request, providing the template's ID value
-     * @param int $id
-     * @param Template $Template
+     * Update one specific template resource with a PUT request, providing the template's ID value.
+     *
+     * @param string   $id
+     * @param Template $template
+     *
+     * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function update($id, Template $Template)
+    public function update(string $id, Template $template): array
     {
-        $response = $this->mailjet->put(Resources::$Template,
-            ['id' => $id, 'body' => $Template->format()]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService:update() failed", $response);
+        $response = $this->mailjet->put(Resources::$Template, ['id' => $id, 'body' => $template->format()]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:update() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * delete a given template
+     * Delete a given template.
+     *
      * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function delete($id)
+    public function delete(string $id): array
     {
         $response = $this->mailjet->delete(Resources::$Template, ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService:delete() failed", $response);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:delete() failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Return the text and html contents of the Template
+     * Return the text and html contents of the Template.
+     *
      * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function getDetailContent($id)
+    public function getDetailContent(string $id): array
     {
-        $response = $this->mailjet->get(Resources::$TemplateDetailcontent,
-            ['id' => $id]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService:getDetailContent failed",
-                $response);
+        $response = $this->mailjet->get(Resources::$TemplateDetailcontent, ['id' => $id]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:getDetailContent failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Creates the content of a  Template
+     * Creates the content of a Template.
+     *
+     * @param string $id
+     * @param array  $content
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function createDetailContent($id, $contentData)
+    public function createDetailContent(string $id, array $content): array
     {
-        $response = $this->mailjet->post(Resources::$TemplateDetailcontent,
-            ['id' => $id, 'body' => $contentData]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService:createDetailContent failed",
-                $response);
+        $response = $this->mailjet->post(Resources::$TemplateDetailcontent, ['id' => $id, 'body' => $content]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:createDetailContent failed', $response);
         }
 
         return $response->getData();
     }
 
     /**
-     * Deletes the content of a  Template
+     * Deletes the content of a Template.
+     *
+     * @param string $id
+     *
      * @return array
+     * @throws \Mailjet\LaravelMailjet\Exception\MailjetException
      */
-    public function deleteDetailContent($id)
+    public function deleteDetailContent(string $id): array
     {
-        $nullContent = null;
-        $response    = $this->mailjet->post(Resources::$TemplateDetailcontent,
-            ['id' => $id, 'body' => $nullContent]);
-        if (!$response->success()) {
-            $this->throwError("TemplateService:createDetailContent failed",
-                $response);
+        $response = $this->mailjet->post(Resources::$TemplateDetailcontent, ['id' => $id, 'body' => null]);
+
+        if (! $response->success()) {
+            throw new MailjetException(0, 'TemplateService:createDetailContent failed', $response);
         }
 
         return $response->getData();
     }
-
-    private function throwError($title, Response $response)
-    {
-        throw new MailjetException(0, $title, $response);
-    }
-}
\ No newline at end of file
+}
diff --git a/src/Transport/MailjetTransport.php b/src/Transport/MailjetTransport.php
index a99bd22..9c21ec4 100644
--- a/src/Transport/MailjetTransport.php
+++ b/src/Transport/MailjetTransport.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Transport;
 
 use Mailjet\MailjetSwiftMailer\SwiftMailer\MailjetTransport as BaseTransport;
diff --git a/tests/Providers/CampaignDraftServiceProviderTest.php b/tests/Providers/CampaignDraftServiceProviderTest.php
index c97344a..b522b40 100644
--- a/tests/Providers/CampaignDraftServiceProviderTest.php
+++ b/tests/Providers/CampaignDraftServiceProviderTest.php
@@ -1,62 +1,64 @@
 <?php
 
-namespace Mailjet\LaravelMailjet\Tests\Services;
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Tests\Providers;
 
-use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Support\ServiceProvider;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Contracts\Foundation\Application;
 use Mailjet\LaravelMailjet\Providers\CampaignDraftServiceProvider;
+use Mailjet\LaravelMailjet\Contracts\CampaignDraftContract;
 
 class CampaignDraftServiceProviderTest extends TestCase
 {
     /**
-     * @var Mockery\Mock
+     * @var Application|Mockery\Mock
      */
-    protected $application_mock;
+    protected $application;
 
     /**
      * @var ServiceProvider
      */
-    protected $service_provider;
+    protected $serviceProvider;
 
     protected function setUp(): void
     {
         $this->setUpMocks();
 
-        $this->service_provider = new CampaignDraftServiceProvider($this->application_mock);
+        $this->serviceProvider = new CampaignDraftServiceProvider($this->application);
 
         parent::setUp();
     }
 
-    protected function setUpMocks()
-    {
-        $this->application_mock = Mockery::mock(Application::class);
-        $this->application_mock->shouldReceive('bind');
-    }
-
     /**
      * @test
      */
-    public function it_can_be_constructed()
+    public function it_can_be_constructed(): void
     {
-        $this->assertInstanceOf(ServiceProvider::class, $this->service_provider);
+        $this->assertInstanceOf(ServiceProvider::class, $this->serviceProvider);
     }
 
     /**
      * @test
      */
-    public function it_does_provide_method()
+    public function it_does_provide_method(): void
     {
-        $this->assertContains('Mailjet\LaravelMailjet\Contracts\CampaignDraftContract', $this->service_provider->provides());
+        $this->assertContains(CampaignDraftContract::class, $this->serviceProvider->provides());
     }
 
     /**
      * @test
      */
-    public function it_performs_nothing_in_a_boot_method()
+    public function it_performs_nothing_in_a_boot_method(): void
+    {
+        $this->assertNull($this->serviceProvider->boot());
+    }
+
+    protected function setUpMocks(): void
     {
-        $this->assertNull($this->service_provider->boot());
-    
+        $this->application = Mockery::mock(Application::class);
+        $this->application->shouldReceive('bind');
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Providers/CampaignServiceProviderTest.php b/tests/Providers/CampaignServiceProviderTest.php
index 2042759..b219f3d 100644
--- a/tests/Providers/CampaignServiceProviderTest.php
+++ b/tests/Providers/CampaignServiceProviderTest.php
@@ -1,62 +1,64 @@
 <?php
 
-namespace Mailjet\LaravelMailjet\Tests\Services;
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Tests\Providers;
 
-use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Support\ServiceProvider;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Contracts\Foundation\Application;
+use Mailjet\LaravelMailjet\Contracts\CampaignContract;
 use Mailjet\LaravelMailjet\Providers\CampaignServiceProvider;
 
-class CampaigntServiceProviderTest extends TestCase
+class CampaignServiceProviderTest extends TestCase
 {
     /**
-     * @var Mockery\Mock
+     * @var Application|Mockery\Mock
      */
-    protected $application_mock;
+    protected $application;
 
     /**
      * @var ServiceProvider
      */
-    protected $service_provider;
+    protected $serviceProvider;
 
     protected function setUp(): void
     {
         $this->setUpMocks();
 
-        $this->service_provider = new CampaignServiceProvider($this->application_mock);
+        $this->serviceProvider = new CampaignServiceProvider($this->application);
 
         parent::setUp();
     }
 
-    protected function setUpMocks()
-    {
-        $this->application_mock = Mockery::mock(Application::class);
-        $this->application_mock->shouldReceive('bind');
-    }
-
     /**
      * @test
      */
-    public function it_can_be_constructed()
+    public function it_can_be_constructed(): void
     {
-        $this->assertInstanceOf(ServiceProvider::class, $this->service_provider);
+        $this->assertInstanceOf(ServiceProvider::class, $this->serviceProvider);
     }
 
     /**
      * @test
      */
-    public function it_does_provide_method()
+    public function it_does_provide_method(): void
     {
-        $this->assertContains('Mailjet\LaravelMailjet\Contracts\CampaignContract', $this->service_provider->provides());
+        $this->assertContains(CampaignContract::class, $this->serviceProvider->provides());
     }
 
     /**
      * @test
      */
-    public function it_performs_nothing_in_a_boot_method()
+    public function it_performs_nothing_in_a_boot_method(): void
+    {
+        $this->assertNull($this->serviceProvider->boot());
+    }
+
+    protected function setUpMocks(): void
     {
-        $this->assertNull($this->service_provider->boot());
-    
+        $this->application = Mockery::mock(Application::class);
+        $this->application->shouldReceive('bind');
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Providers/ContactMetadataServiceProviderTest.php b/tests/Providers/ContactMetadataServiceProviderTest.php
index 43077f7..789551c 100644
--- a/tests/Providers/ContactMetadataServiceProviderTest.php
+++ b/tests/Providers/ContactMetadataServiceProviderTest.php
@@ -1,62 +1,64 @@
 <?php
 
-namespace Mailjet\LaravelMailjet\Tests\Services;
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Tests\Providers;
 
-use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Support\ServiceProvider;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Contracts\Foundation\Application;
 use Mailjet\LaravelMailjet\Providers\ContactMetadataServiceProvider;
+use Mailjet\LaravelMailjet\Contracts\ContactMetadataContract;
 
 class ContactMetadataServiceProviderTest extends TestCase
 {
     /**
-     * @var Mockery\Mock
+     * @var Application|Mockery\Mock
      */
-    protected $application_mock;
+    protected $application;
 
     /**
      * @var ServiceProvider
      */
-    protected $service_provider;
+    protected $serviceProvider;
 
     protected function setUp(): void
     {
         $this->setUpMocks();
 
-        $this->service_provider = new ContactMetadataServiceProvider($this->application_mock);
+        $this->serviceProvider = new ContactMetadataServiceProvider($this->application);
 
         parent::setUp();
     }
 
-    protected function setUpMocks()
-    {
-        $this->application_mock = Mockery::mock(Application::class);
-        $this->application_mock->shouldReceive('bind');
-    }
-
     /**
      * @test
      */
-    public function it_can_be_constructed()
+    public function it_can_be_constructed(): void
     {
-        $this->assertInstanceOf(ServiceProvider::class, $this->service_provider);
+        $this->assertInstanceOf(ServiceProvider::class, $this->serviceProvider);
     }
 
     /**
      * @test
      */
-    public function it_does_provide_method()
+    public function it_does_provide_method(): void
     {
-        $this->assertContains('Mailjet\LaravelMailjet\Contracts\ContactMetadataContract', $this->service_provider->provides());
+        $this->assertContains(ContactMetadataContract::class, $this->serviceProvider->provides());
     }
 
     /**
      * @test
      */
-    public function it_performs_nothing_in_a_boot_method()
+    public function it_performs_nothing_in_a_boot_method(): void
+    {
+        $this->assertNull($this->serviceProvider->boot());
+    }
+
+    protected function setUpMocks(): void
     {
-        $this->assertNull($this->service_provider->boot());
-    
+        $this->application = Mockery::mock(Application::class);
+        $this->application->shouldReceive('bind');
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Providers/ContactsListServiceProviderTest.php b/tests/Providers/ContactsListServiceProviderTest.php
index d6d7ee8..fb9436d 100644
--- a/tests/Providers/ContactsListServiceProviderTest.php
+++ b/tests/Providers/ContactsListServiceProviderTest.php
@@ -1,62 +1,64 @@
 <?php
 
-namespace Mailjet\LaravelMailjet\Tests\Services;
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Tests\Providers;
 
-use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Support\ServiceProvider;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Contracts\Foundation\Application;
 use Mailjet\LaravelMailjet\Providers\ContactsListServiceProvider;
+use Mailjet\LaravelMailjet\Contracts\ContactsListContract;
 
 class ContactsListServiceProviderTest extends TestCase
 {
     /**
-     * @var Mockery\Mock
+     * @var Application|Mockery\Mock
      */
-    protected $application_mock;
+    protected $application;
 
     /**
      * @var ServiceProvider
      */
-    protected $service_provider;
+    protected $serviceProvider;
 
     protected function setUp(): void
     {
         $this->setUpMocks();
 
-        $this->service_provider = new ContactsListServiceProvider($this->application_mock);
+        $this->serviceProvider = new ContactsListServiceProvider($this->application);
 
         parent::setUp();
     }
 
-    protected function setUpMocks()
-    {
-        $this->application_mock = Mockery::mock(Application::class);
-        $this->application_mock->shouldReceive('bind');
-    }
-
     /**
      * @test
      */
-    public function it_can_be_constructed()
+    public function it_can_be_constructed(): void
     {
-        $this->assertInstanceOf(ServiceProvider::class, $this->service_provider);
+        $this->assertInstanceOf(ServiceProvider::class, $this->serviceProvider);
     }
 
     /**
      * @test
      */
-    public function it_does_provide_method()
+    public function it_does_provide_method(): void
     {
-        $this->assertContains('Mailjet\LaravelMailjet\Contracts\ContactsListContract', $this->service_provider->provides());
+        $this->assertContains(ContactsListContract::class, $this->serviceProvider->provides());
     }
 
     /**
      * @test
      */
-    public function it_performs_nothing_in_a_boot_method()
+    public function it_performs_nothing_in_a_boot_method(): void
+    {
+        $this->assertNull($this->serviceProvider->boot());
+    }
+
+    protected function setUpMocks(): void
     {
-        $this->assertNull($this->service_provider->boot());
-    
+        $this->application = Mockery::mock(Application::class);
+        $this->application->shouldReceive('bind');
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Providers/EventCallbackUrlServiceProviderTest.php b/tests/Providers/EventCallbackUrlServiceProviderTest.php
index eb6eb7d..eb2ebdd 100644
--- a/tests/Providers/EventCallbackUrlServiceProviderTest.php
+++ b/tests/Providers/EventCallbackUrlServiceProviderTest.php
@@ -1,62 +1,64 @@
 <?php
 
-namespace Mailjet\LaravelMailjet\Tests\Services;
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Tests\Providers;
 
-use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Support\ServiceProvider;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Contracts\Foundation\Application;
+use Mailjet\LaravelMailjet\Contracts\EventCallbackUrlContract;
 use Mailjet\LaravelMailjet\Providers\EventCallbackUrlServiceProvider;
 
 class EventCallbackUrlServiceProviderTest extends TestCase
 {
     /**
-     * @var Mockery\Mock
+     * @var Application|Mockery\Mock
      */
-    protected $application_mock;
+    protected $application;
 
     /**
      * @var ServiceProvider
      */
-    protected $service_provider;
+    protected $serviceProvider;
 
     protected function setUp(): void
     {
         $this->setUpMocks();
 
-        $this->service_provider = new EventCallbackUrlServiceProvider($this->application_mock);
+        $this->serviceProvider = new EventCallbackUrlServiceProvider($this->application);
 
         parent::setUp();
     }
 
-    protected function setUpMocks()
-    {
-        $this->application_mock = Mockery::mock(Application::class);
-        $this->application_mock->shouldReceive('bind');
-    }
-
     /**
      * @test
      */
-    public function it_can_be_constructed()
+    public function it_can_be_constructed(): void
     {
-        $this->assertInstanceOf(ServiceProvider::class, $this->service_provider);
+        $this->assertInstanceOf(ServiceProvider::class, $this->serviceProvider);
     }
 
     /**
      * @test
      */
-    public function it_does_provide_method()
+    public function it_does_provide_method(): void
     {
-        $this->assertContains('Mailjet\LaravelMailjet\Contracts\EventCallbackUrlContract', $this->service_provider->provides());
+        $this->assertContains(EventCallbackUrlContract::class, $this->serviceProvider->provides());
     }
 
     /**
      * @test
      */
-    public function it_performs_nothing_in_a_boot_method()
+    public function it_performs_nothing_in_a_boot_method(): void
+    {
+        $this->assertNull($this->serviceProvider->boot());
+    }
+
+    protected function setUpMocks(): void
     {
-        $this->assertNull($this->service_provider->boot());
-    
+        $this->application = Mockery::mock(Application::class);
+        $this->application->shouldReceive('bind');
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Providers/MailjetClientServiceProviderTest.php b/tests/Providers/MailjetClientServiceProviderTest.php
index 5f35a31..ea8b1f8 100644
--- a/tests/Providers/MailjetClientServiceProviderTest.php
+++ b/tests/Providers/MailjetClientServiceProviderTest.php
@@ -1,62 +1,64 @@
 <?php
 
-namespace Mailjet\LaravelMailjet\Tests\Services;
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Tests\Providers;
 
-use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Support\ServiceProvider;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Contracts\Foundation\Application;
 use Mailjet\LaravelMailjet\Providers\MailjetClientServiceProvider;
+use Mailjet\LaravelMailjet\Contracts\MailjetServiceContract;
 
 class MailjetClientServiceProviderTest extends TestCase
 {
     /**
-     * @var Mockery\Mock
+     * @var Application|Mockery\Mock
      */
-    protected $application_mock;
+    protected $application;
 
     /**
      * @var ServiceProvider
      */
-    protected $service_provider;
+    protected $serviceProvider;
 
     protected function setUp(): void
     {
         $this->setUpMocks();
 
-        $this->service_provider = new MailjetClientServiceProvider($this->application_mock);
+        $this->serviceProvider = new MailjetClientServiceProvider($this->application);
 
         parent::setUp();
     }
 
-    protected function setUpMocks()
-    {
-        $this->application_mock = Mockery::mock(Application::class);
-        $this->application_mock->shouldReceive('bind');
-    }
-
     /**
      * @test
      */
-    public function it_can_be_constructed()
+    public function it_can_be_constructed(): void
     {
-        $this->assertInstanceOf(ServiceProvider::class, $this->service_provider);
+        $this->assertInstanceOf(ServiceProvider::class, $this->serviceProvider);
     }
 
     /**
      * @test
      */
-    public function it_does_provide_method()
+    public function it_does_provide_method(): void
     {
-        $this->assertContains('Mailjet\LaravelMailjet\Contracts\MailjetServiceContract', $this->service_provider->provides());
+        $this->assertContains(MailjetServiceContract::class, $this->serviceProvider->provides());
     }
 
     /**
      * @test
      */
-    public function it_performs_nothing_in_a_boot_method()
+    public function it_performs_nothing_in_a_boot_method(): void
+    {
+        $this->assertNull($this->serviceProvider->boot());
+    }
+
+    protected function setUpMocks(): void
     {
-        $this->assertNull($this->service_provider->boot());
-    
+        $this->application = Mockery::mock(Application::class);
+        $this->application->shouldReceive('bind');
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Providers/TemplateServiceProviderTest.php b/tests/Providers/TemplateServiceProviderTest.php
index b1a8356..00a669d 100644
--- a/tests/Providers/TemplateServiceProviderTest.php
+++ b/tests/Providers/TemplateServiceProviderTest.php
@@ -1,62 +1,64 @@
 <?php
 
-namespace Mailjet\LaravelMailjet\Tests\Services;
+declare(strict_types=1);
+
+namespace Mailjet\LaravelMailjet\Tests\Providers;
 
-use Illuminate\Contracts\Foundation\Application;
-use Illuminate\Support\ServiceProvider;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Contracts\Foundation\Application;
 use Mailjet\LaravelMailjet\Providers\TemplateServiceProvider;
+use Mailjet\LaravelMailjet\Contracts\TemplateServiceContract;
 
 class TemplateServiceProviderTest extends TestCase
 {
     /**
-     * @var Mockery\Mock
+     * @var Application|Mockery\Mock
      */
-    protected $application_mock;
+    protected $application;
 
     /**
      * @var ServiceProvider
      */
-    protected $service_provider;
+    protected $serviceProvider;
 
     protected function setUp(): void
     {
         $this->setUpMocks();
 
-        $this->service_provider = new TemplateServiceProvider($this->application_mock);
+        $this->serviceProvider = new TemplateServiceProvider($this->application);
 
         parent::setUp();
     }
 
-    protected function setUpMocks()
-    {
-        $this->application_mock = Mockery::mock(Application::class);
-        $this->application_mock->shouldReceive('bind');
-    }
-
     /**
      * @test
      */
-    public function it_can_be_constructed()
+    public function it_can_be_constructed(): void
     {
-        $this->assertInstanceOf(ServiceProvider::class, $this->service_provider);
+        $this->assertInstanceOf(ServiceProvider::class, $this->serviceProvider);
     }
 
     /**
      * @test
      */
-    public function it_does_provide_method()
+    public function it_does_provide_method(): void
     {
-        $this->assertContains('Mailjet\LaravelMailjet\Contracts\TemplateServiceContract', $this->service_provider->provides());
+        $this->assertContains(TemplateServiceContract::class, $this->serviceProvider->provides());
     }
 
     /**
      * @test
      */
-    public function it_performs_nothing_in_a_boot_method()
+    public function it_performs_nothing_in_a_boot_method(): void
+    {
+        $this->assertNull($this->serviceProvider->boot());
+    }
+
+    protected function setUpMocks(): void
     {
-        $this->assertNull($this->service_provider->boot());
-    
+        $this->application = Mockery::mock(Application::class);
+        $this->application->shouldReceive('bind');
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Services/MailjetServiceTest.php b/tests/Services/MailjetServiceTest.php
index 4cff008..ef48078 100644
--- a/tests/Services/MailjetServiceTest.php
+++ b/tests/Services/MailjetServiceTest.php
@@ -1,13 +1,16 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Mailjet\LaravelMailjet\Tests\Services;
 
 use Mailjet\Client;
 use Mailjet\LaravelMailjet\Services\MailjetService;
-use Mailjet\Resources;
 use Mailjet\Response;
 use Mockery;
 use Orchestra\Testbench\TestCase;
+use Mailjet\LaravelMailjet\Facades\Mailjet;
+use Mailjet\LaravelMailjet\MailjetServiceProvider;
 
 class MailjetServiceTest extends TestCase
 {
@@ -35,14 +38,14 @@ public function setUp(): void
             ->andReturnUsing(function($resourceArg, $params) use ($responseMock) {
                 $data = [];
 
-                switch ($resourceArg) {
+                switch ($resourceArg[0]) {
                     case 'resource-test-put':
                         $data = array_merge($params, [
                             'status' => '0003',
                         ]);
                         break;
 
-                    case Resources::$Listrecipient:
+                    case 'listrecipient':
                         $data = array_merge($params, [
                             'status' => '0011',
                         ]);
@@ -59,26 +62,26 @@ public function setUp(): void
             ->andReturnUsing(function($resourceArg, $params) use ($responseMock) {
                 $data = [];
 
-                switch ($resourceArg) {
+                switch ($resourceArg[0]) {
                     case 'resource-test-post':
                         $data = array_merge($params, [
                             'status' => '0001',
                         ]);
                         break;
 
-                    case Resources::$Contactslist:
+                    case 'contactslist':
                         $data = array_merge($params, [
                             'status' => '0006',
                         ]);
                         break;
 
-                    case Resources::$Contact:
+                    case 'contact':
                         $data = array_merge($params, [
                             'status' => '0009',
                         ]);
                         break;
 
-                    case Resources::$Listrecipient:
+                    case 'listrecipient':
                         $data = array_merge($params, [
                             'status' => '0010',
                         ]);
@@ -96,7 +99,7 @@ public function setUp(): void
             ->andReturnUsing(function($resourceArg, $params) use ($responseMock) {
                 $data = [];
 
-                switch ($resourceArg) {
+                switch ($resourceArg[0]) {
                     case 'resource-test-delete':
                         $data = array_merge($params, [
                             'status' => '0004',
@@ -114,26 +117,26 @@ public function setUp(): void
             ->andReturnUsing(function($resourceArg, $params) use ($responseMock) {
                 $data = [];
 
-                switch ($resourceArg) {
+                switch ($resourceArg[0]) {
                     case 'resource-test-get':
                         $data = array_merge($params, [
                             'status' => '0002',
                         ]);
                         break;
 
-                    case Resources::$Contactslist:
+                    case 'contactslist':
                         $data = array_merge($params, [
                             'status' => '0005',
                         ]);
                         break;
 
-                    case Resources::$Listrecipient:
+                    case 'listrecipient':
                         $data = array_merge($params, [
                             'status' => '0007',
                         ]);
                         break;
 
-                    case Resources::$Contact:
+                    case 'contact':
                         $data = array_merge($params, [
                             'status' => '0008',
                         ]);
@@ -148,7 +151,7 @@ public function setUp(): void
         $this->mailjetService = $this->app['Mailjet'];
     }
 
-    public function testFacade()
+    public function testFacade(): void
     {
         $this->assertTrue(method_exists($this->mailjetService, 'get'));
         $this->assertTrue(method_exists($this->mailjetService, 'post'));
@@ -164,15 +167,15 @@ public function testFacade()
         $this->assertTrue(method_exists($this->mailjetService, 'getClient'));
     }
 
-    public function testCanUseClient()
+    public function testCanUseClient(): void
     {
-        $client = \Mailjet::getClient();
-        $this->assertEquals("Mailjet\Client", get_class($client));
+        $client = Mailjet::getClient();
+        $this->assertInstanceOf(Client::class, $client);
     }
 
     public function testPost()
     {
-        $response = $this->mailjetService->post('resource-test-post', [
+        $response = $this->mailjetService->post(['resource-test-post'], [
             'data' => 'test0001',
         ]);
 
@@ -184,7 +187,7 @@ public function testPost()
 
     public function testGet()
     {
-        $response = $this->mailjetService->get('resource-test-get', [
+        $response = $this->mailjetService->get(['resource-test-get'], [
             'data' => 'test0002',
         ], []);
 
@@ -196,7 +199,7 @@ public function testGet()
 
     public function testPut()
     {
-        $response = $this->mailjetService->put('resource-test-put', [
+        $response = $this->mailjetService->put(['resource-test-put'], [
             'data' => 'test0003',
         ], []);
 
@@ -208,7 +211,7 @@ public function testPut()
 
     public function testDelete()
     {
-        $response = $this->mailjetService->delete('resource-test-delete', [
+        $response = $this->mailjetService->delete(['resource-test-delete'], [
             'data' => 'test0004',
         ], []);
 
@@ -262,10 +265,10 @@ public function testGetListRecipients()
 
     public function testGetSingleContact()
     {
-        $response = $this->mailjetService->getSingleContact(123);
+        $response = $this->mailjetService->getSingleContact('123');
 
         $this->assertSame([
-            'id' => 123,
+            'id' => '123',
             'status' => '0008',
         ], $response->getData());
     }
@@ -300,12 +303,12 @@ public function testCreateListRecipient()
 
     public function testEditListrecipient()
     {
-        $response = $this->mailjetService->editListrecipient(123, [
+        $response = $this->mailjetService->editListrecipient('1233', [
             'data' => 'test0011'
         ]);
 
         $this->assertSame([
-            'id' => 123,
+            'id' => '1233',
             'body' => [
                 'data' => 'test0011',
             ],
@@ -313,10 +316,10 @@ public function testEditListrecipient()
         ], $response->getData());
     }
 
-    protected function getPackageAliases($app)
+    protected function getPackageAliases($app): array
     {
         return [
-            'Mailjet' => \Mailjet\LaravelMailjet\Facades\Mailjet::class
+            'Mailjet' => Mailjet::class
         ];
     }
 
@@ -326,15 +329,15 @@ protected function getPackageAliases($app)
      * @param  \Illuminate\Foundation\Application  $app
      * @return void
      */
-    protected function getEnvironmentSetUp($app)
+    protected function getEnvironmentSetUp($app): void
     {
         // Setup default database to use sqlite :memory:
         $app['config']->set('services.mailjet.key', 'ABC123456');
         $app['config']->set('services.mailjet.secret', 'ABC123456');
     }
 
-    protected function getPackageProviders($app)
+    protected function getPackageProviders($app): array
     {
-        return ['\Mailjet\LaravelMailjet\MailjetServiceProvider'];
+        return [MailjetServiceProvider::class];
     }
 }
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 65b7b04..5fb6079 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,2 +1,5 @@
 <?php
+
+declare(strict_types=1);
+
 require_once(__DIR__ . '/../vendor/autoload.php');