diff --git a/.github/workflows/citests.yml b/.github/workflows/citests.yml
index 26fd37f..93ad7f5 100644
--- a/.github/workflows/citests.yml
+++ b/.github/workflows/citests.yml
@@ -18,7 +18,9 @@ jobs:
         extensions: xml, curl, dom, mbstring
     - name: Install Composer dependencies
       run: composer install
-    - name: Running unit test
-      run: ./vendor/bin/phpunit Tests
+    - name: Running unit tests
+      run: ./vendor/bin/phpunit Tests/Unit
+    - name: Running integration tests
+      run: ./vendor/bin/phpunit Tests/Int
       env:
         API_KEY: ${{ secrets.API_KEY }}
diff --git a/Payload/API.php b/Payload/API.php
index 18cfca0..15feebc 100644
--- a/Payload/API.php
+++ b/Payload/API.php
@@ -1,15 +1,17 @@
 <?php
 namespace Payload;
+
 require_once('Attr.php');
 
-class API {
-    const version = '0.4.0';
+class API
+{
+    const version = '1.0.0';
     public static $api_key;
     public static $api_url = 'https://api.payload.com';
     public static $api_version;
-    public static function __callStatic($name, $arguments) {
-        assert( $name == 'attr' );
+    public static function __callStatic($name, $arguments)
+    {
+        assert($name == 'attr');
         return new Attr();
     }
 }
-?>
diff --git a/Payload/ARMObject.php b/Payload/ARMObject.php
index 59313f3..99411bd 100644
--- a/Payload/ARMObject.php
+++ b/Payload/ARMObject.php
@@ -3,14 +3,40 @@
 
 require_once('ARMRequest.php');
 
-class ARMObject {
-    private static $_object_cache = array();
-    public static $spec = array();
-    public static $type = null;
+class ARMObject
+{
+    private static $_object_cache = [];
+    private static $_registry = [];
+    public static $spec = [];
+    private static $_default_params = [];
+
+    public static function setDefaultParams($params) {
+        self::$_default_params[get_called_class()] = $params;
+    }
+
+    public static function getDefaultParams() {
+        return self::$_default_params[get_called_class()] ?? [];
+    }
+
+    public static function getRegistry()
+    {
+        if (empty(self::$_registry)) {
+            foreach (glob(__DIR__ . '/*.php') as $file) {
+                require_once($file);
+            }
+            foreach (get_declared_classes() as $class) {
+                if (is_subclass_of($class, self::class) && isset($class::$spec['object'])) {
+                    self::$_registry[$class::$spec['object']] = $class;
+                }
+            }
+        }
+        return self::$_registry;
+    }
 
-    public static function new($data) {
+    public static function new($data)
+    {
         $class = get_called_class();
-        if ( isset($data['id']) && isset(self::$_object_cache[$data['id']]) ) {
+        if (isset($data['id']) && isset(self::$_object_cache[$data['id']])) {
             $cached_object = self::$_object_cache[$data['id']];
             $cached_object->data($data);
             return $cached_object;
@@ -18,80 +44,129 @@ public static function new($data) {
         return new $class($data);
     }
 
-    function __construct($data) {
-        if ($data !== null)
+    function __construct($data)
+    {
+        if ($data !== null) {
             $this->data($data);
+        }
+    }
+
+    private static function _build_request($cls = null, $apply_polymorphic = false)
+    {
+        $cls = $cls ?: get_called_class();
+        $req = new ARMRequest($cls);
+        if ($apply_polymorphic && isset($cls::$spec['polymorphic_type'])) {
+            $req->filter_by(['type' => $cls::$spec['polymorphic_type']]);
+        }
+        return $req;
     }
 
-    public function __get($name) {
-        if (array_key_exists($name, $this->_data))
+    public function __get($name)
+    {
+        if (array_key_exists($name, $this->_data)) {
             return $this->_data[$name];
-        else
+        } else {
             throw new \Exception("$name does not exist");
+        }
     }
 
-    public function json() {
+    public function json()
+    {
         return json_encode($this->data(), JSON_PRETTY_PRINT);
     }
 
 
-    public function data($data=null) {
-        if ( $data !== null ) {
+    public function data($data = null)
+    {
+        if ($data !== null) {
             $this->_data = Utils::data2object($data);
-            if ( isset($data['id']) )
+            if (isset($data['id'])) {
                 self::$_object_cache[$this->id] = $this;
+            }
         } else {
             return Utils::object2data($this->_data);
         }
     }
 
-    public function update($update) {
-        return (new ARMRequest(get_called_class()))->request('put',
-            array('id'=>$this->id, 'json'=>$update));
+    public function update($update)
+    {
+        return static::_build_request(static::class)->request(
+            'put',
+            ['id'=>$this->id, 'json'=>$update]
+        );
     }
 
-    public function delete($update=null) {
-        if ($update !== null){
-            return (new ARMRequest(get_called_class()))->request('delete',
-            array('id'=>$update->id));
+    public function delete($update = null)
+    {
+        if ($update !== null) {
+            return static::_build_request(static::class)->request(
+                'delete',
+                ['id'=>$update->id]
+            );
         } else {
-            return (new ARMRequest(get_called_class()))->request('delete',
-                array('id'=>$this->id));
+            return static::_build_request(static::class)->request(
+                'delete',
+                ['id'=>$this->id]
+            );
         }
     }
 
-    public static function get($id) {
-        return (new ARMRequest(get_called_class()))->get($id);
+    public static function get($id)
+    {
+        return static::_build_request()->get($id);
     }
 
-    public static function filter_by(...$filters) {
-        if ( isset(get_called_class()::$spec['polymorphic_type']) )
-            array_push($filters, ['type' => get_called_class()::$spec['polymorphic_type']]);
+    public static function all()
+    {
+        return static::_build_request()->all();
+    }
 
-        $req = new ARMRequest(get_called_class());
-        return call_user_func_array(array($req, 'filter_by'), $filters);
+    public static function filter_by(...$filters)
+    {
+        $req = static::_build_request(null, true);
+        return call_user_func_array([$req, 'filter_by'], $filters);
     }
 
-    public static function create($obj) {
-        if ( isset(get_called_class()::$spec['polymorphic_type']) )
+    public static function create($obj)
+    {
+        if (isset(get_called_class()::$spec['polymorphic_type'])) {
             $obj['type'] = get_called_class()::$spec['polymorphic_type'];
+        }
 
-        return (new ARMRequest(get_called_class()))->create($obj);
+        return static::_build_request()->create($obj);
     }
 
-    public static function select(...$attrs) {
-        $req = new ARMRequest(get_called_class());
-        return call_user_func_array(array($req, 'select'), $attrs);
+    public static function select(...$attrs)
+    {
+        $req = static::_build_request(null, true);
+        return call_user_func_array([$req, 'select'], $attrs);
     }
 
-    public static function delete_all(...$objs) {
+    public static function order_by(...$attrs)
+    {
+        $req = static::_build_request(null, true);
+        return call_user_func_array([$req, 'order_by'], $attrs);
+    }
+
+    public static function limit($limit)
+    {
+        return static::_build_request(null, true)->limit($limit);
+    }
+
+    public static function offset($offset)
+    {
+        return static::_build_request(null, true)->offset($offset);
+    }
 
-        $func = function($value) {
+    public static function delete_all(...$objs)
+    {
+        $func = function ($value) {
             return $value->id;
         };
 
-        return (new ARMRequest(get_called_class()))->request('delete',
-            array('id'=>join("|",array_map($func, $objs))));
+        return static::_build_request()->request(
+            'delete',
+            ['id'=>join("|", array_map($func, $objs))]
+        );
     }
 }
-?>
diff --git a/Payload/ARMRequest.php b/Payload/ARMRequest.php
index 54c2904..70dea7d 100644
--- a/Payload/ARMRequest.php
+++ b/Payload/ARMRequest.php
@@ -1,145 +1,224 @@
 <?php
 namespace Payload;
+
 use Payload\Utils;
-include('Exceptions.php');
 
-class ARMRequest {
+require_once('Exceptions.php');
+
+class ARMRequest
+{
+    protected $cls;
+    protected $filters = [];
+    protected $attrs = [];
+    protected $group_by = [];
+    protected $order_by = [];
+    protected $limit = null;
+    protected $offset = null;
 
-    function __construct($cls) {
+    function __construct($cls)
+    {
         $this->cls = $cls;
-        $this->filters = array();
-        $this->attrs = array();
-        $this->group_by = array();
     }
 
-    function request($method, $args=array()) {
-        if ( isset($this->cls::$spec['endpoint']) )
+    function request($method, $args = [])
+    {
+        if (isset($this->cls::$spec['endpoint'])) {
             $endpoint = $this->cls::$spec['endpoint'];
-        else
-            $endpoint = '/'.$this->cls::$spec['object'] . 's';
+        } else {
+            $object = $this->cls::$spec['object'];
+            $endpoint = '/'.$object . (substr($object, -1) === 's' ? '' : 's');
+        }
 
-        if (isset($args['id']))
+        if (isset($args['id'])) {
             $endpoint .= '/'.$args['id'];
+        }
 
-        $params = array_merge(array(), $this->filters);
+        $params = array_merge([], $this->filters);
 
-        if (count($this->attrs))
+        if (count($this->attrs)) {
             $params['fields'] = array_map(function ($item) {
                 return strval($item);
             }, $this->attrs);
+        }
 
-        if (count($this->group_by))
-            $params['fields'] = array_map(function ($item) {
+        if (count($this->group_by)) {
+            $params['group_by'] = array_map(function ($item) {
                 return strval($item);
             }, $this->group_by);
+        }
+
+        if (count($this->order_by)) {
+            $params['order_by'] = array_map(function ($item) {
+                return strval($item);
+            }, $this->order_by);
+        }
 
-        if (isset($args['mode']))
+        if (isset($this->limit)) {
+            $params['limit'] = $this->limit;
+        }
+
+        if (isset($this->offset)) {
+            $params['offset'] = $this->offset;
+        }
+
+        if (isset($args['mode'])) {
             $params['mode'] = $args['mode'];
+        }
 
-        if (count($params))
+        $defaults = $this->cls::getDefaultParams();
+        if ($defaults) {
+            foreach ($defaults as $k => $v) {
+                if (!isset($params[$k])) {
+                    $params[$k] = $v;
+                }
+            }
+        }
+
+        if (count($params)) {
             $endpoint .= '?'.http_build_query($params, '', '&');
+        }
 
         $req = curl_init(API::$api_url . $endpoint);
         curl_setopt($req, CURLOPT_CUSTOMREQUEST, strtoupper($method));
         curl_setopt($req, CURLOPT_USERPWD, API::$api_key . ':');
         curl_setopt($req, CURLOPT_RETURNTRANSFER, true);
 
-        $headers = array();
+        $headers = [];
 
         if (isset($args['json'])) {
-           $json = json_encode($args['json']);
-           curl_setopt($req, CURLOPT_POSTFIELDS, $json);
-           $headers[] = 'Content-Type: application/json';
-           $headers[] = 'Content-Length: '.strlen($json);
+            $json = json_encode($args['json']);
+            curl_setopt($req, CURLOPT_POSTFIELDS, $json);
+            $headers[] = 'Content-Type: application/json';
+            $headers[] = 'Content-Length: '.strlen($json);
         }
 
         if (isset(API::$api_version)) {
-           $headers[] = 'X-API-Version: '.API::$api_version;
+            $headers[] = 'X-API-Version: '.API::$api_version;
         }
 
         if (count($headers) > 0) {
-           curl_setopt($req, CURLOPT_HTTPHEADER, $headers);
+            curl_setopt($req, CURLOPT_HTTPHEADER, $headers);
         }
 
-        $resp    = curl_exec($req);
+        $resp = curl_exec($req);
         $status_code = curl_getinfo($req, CURLINFO_HTTP_CODE);
         curl_close($req);
 
         $result = json_decode($resp, true);
-        if ( $result === null ) {
-            if ( $status_code == 500 ) throw new Exceptions\InternalServerError();
+        if ($result === null) {
+            if ($status_code == 500) {
+                throw new Exceptions\InternalServerError();
+            }
             throw new Exceptions\UnknownResponse();
         }
 
-        if ( !isset($result['object']) )
+        if (!isset($result['object'])) {
             return $result;
+        }
 
-        if ( $status_code == 200 ) {
-            if ( $result['object'] == 'list' )
-                return array_map(function($item) { return $this->cls::new($item); },
+        if ($status_code == 200) {
+            if ($result['object'] == 'list') {
+                return array_map(function ($item) {
+                    return $this->cls::new($item);
+                },
                     $result['values']);
+            }
             return $this->cls::new($result);
         }
 
-        if ( $result['object'] == 'error' ) {
-            foreach( Utils::subclasses(Exceptions\PayloadError::class) as $exc ) {
-                if ( $exc::getClassName() != $result['error_type']) continue;
-                throw new $exc($result['error_description'], $result);
+        if ($result['object'] == 'error') {
+            foreach (get_declared_classes() as $cls) {
+                if (!is_subclass_of($cls, Exceptions\PayloadError::class)) {
+                    continue;
+                }
+                if ($cls::getClassName() != $result['error_type']) {
+                    continue;
+                }
+                throw new $cls($result['error_description'], $result);
             }
             throw new Exceptions\BadRequest($result['error_description'], $result);
         }
 
         throw new Exceptions\UnknownResponse();
-
     }
 
-    public function get($id) {
-        return self::request('GET', array('id'=>$id));
+    public function get($id)
+    {
+        return self::request('GET', ['id'=>$id]);
     }
 
-    public function select(...$attrs) {
+    public function select(...$attrs)
+    {
         $this->attrs = array_merge($this->attrs, $attrs);
         return $this;
     }
 
-    public function group_by(...$attrs) {
+    public function group_by(...$attrs)
+    {
         $this->group_by = array_merge($this->group_by, $attrs);
         return $this;
     }
 
-    public function create($obj) {
-        if ( !Utils::is_assoc_array( $obj ) )
-            $obj = array('object'=>'list', 'values'=>$obj);
+    public function order_by(...$attrs)
+    {
+        $this->order_by = array_merge($this->order_by, $attrs);
+        return $this;
+    }
+
+    public function limit($limit)
+    {
+        $this->limit = $limit;
+        return $this;
+    }
+
+    public function offset($offset)
+    {
+        $this->offset = $offset;
+        return $this;
+    }
+
+    public function create($obj)
+    {
+        if (!Utils::is_assoc_array($obj)) {
+            $obj = ['object'=>'list', 'values'=>$obj];
+        }
         $obj = Utils::object2data($obj);
-        return self::request('POST', array('json'=>$obj));
+        return self::request('POST', ['json'=>$obj]);
     }
 
-    public function delete($obj) {
-        if ( !Utils::is_assoc_array( $obj ) )
-            $obj = array('object'=>'list', 'values'=>$obj);
+    public function delete($obj)
+    {
+        if (!Utils::is_assoc_array($obj)) {
+            $obj = ['object'=>'list', 'values'=>$obj];
+        }
         $obj = Utils::object2data($obj);
-        return self::request('DELETE', array('json'=>$obj, 'mode'=>'query'));
+        return self::request('DELETE', ['json'=>$obj, 'mode'=>'query']);
     }
 
-    public function update($obj) {
-        if ( !Utils::is_assoc_array( $obj ) )
-            $obj = array('object'=>'list', 'values'=>$obj);
-        if ( $obj instanceof ARMObject )
+    public function update($obj)
+    {
+        if (!Utils::is_assoc_array($obj)) {
+            $obj = ['object'=>'list', 'values'=>$obj];
+        }
+        if ($obj instanceof ARMObject) {
             $obj = $obj->data();
-        else
+        } else {
             $obj = Utils::object2data($obj);
-        return self::request('PUT', array('json'=>$obj, 'mode'=>'query'));
+        }
+        return self::request('PUT', ['json'=>$obj, 'mode'=>'query']);
     }
 
-    public function filter_by(...$filters) {
-        $filters = call_user_func_array('array_merge', $filters);
-        $this->filters = array_merge($filters, $this->filters);
+    public function filter_by(...$filters)
+    {
+        if (count($filters)) {
+            $filters = call_user_func_array('array_merge', $filters);
+            $this->filters = array_merge($filters, $this->filters);
+        }
         return $this;
     }
 
-    public function all() {
+    public function all()
+    {
         return $this->request('get');
     }
 }
-
-?>
diff --git a/Payload/AccessToken.php b/Payload/AccessToken.php
index 2eed789..b037eea 100644
--- a/Payload/AccessToken.php
+++ b/Payload/AccessToken.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class AccessToken extends ARMObject {
-    public static $spec = array('object'=>'access_token');
+class AccessToken extends ARMObject
+{
+    public static $spec = ['object'=>'access_token'];
 }
-?>
diff --git a/Payload/Account.php b/Payload/Account.php
index 9db2d10..d6414de 100644
--- a/Payload/Account.php
+++ b/Payload/Account.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Account extends ARMObject {
-    public static $spec = array('object'=>'account');
+class Account extends ARMObject
+{
+    public static $spec = ['object'=>'account'];
 }
-?>
diff --git a/Payload/Attr.php b/Payload/Attr.php
index 9f8125d..525dfce 100644
--- a/Payload/Attr.php
+++ b/Payload/Attr.php
@@ -1,58 +1,74 @@
 <?php
 namespace Payload;
 
-class Attr {
+class Attr
+{
     private $is_method = false;
 
-    function __construct($param=null, $parent=null) {
+    function __construct($param = null, $parent = null)
+    {
         $this->param = $param;
         $this->parent = $parent;
 
-        if ( !$this->parent || !$this->parent->key )
+        if (!$this->parent || !$this->parent->key) {
             $this->key = $this->param;
-        else
+        } else {
             $this->key = $this->parent->key . '[' . $this->param . ']';
+        }
     }
 
-    public function __get($key) {
+    public function __get($key)
+    {
         return new Attr($key, $this);
     }
 
-    public function __toString() {
-        if ($this->is_method)
+    public function __toString()
+    {
+        if ($this->is_method) {
             return $this->param . '(' . $this->parent->key . ')';
-        return $this->key;
+        }
+        return $this->key ?? '';
     }
 
-    public function eq($val) {
-        $ret = array();
+    public function eq($val)
+    {
+        $ret = [];
         $ret[strval($this)] = $val;
         return $ret;
     }
 
-    public function ne($val) {
+    public function ne($val)
+    {
         return $this->eq('!'.$val);
     }
 
-    public function lt($val) {
+    public function lt($val)
+    {
         return $this->eq('<'.$val);
     }
 
-    public function le($val) {
+    public function le($val)
+    {
         return $this->eq('<='.$val);
     }
 
-    public function gt($val) {
+    public function gt($val)
+    {
         return $this->eq('>'.$val);
     }
 
-    public function ge($val) {
+    public function ge($val)
+    {
         return $this->eq('>='.$val);
     }
 
-    public function contains($val) {
+    public function contains($val)
+    {
         return $this->eq('?*'.$val.'*');
     }
-}
 
-?>
+    public function in(...$vals)
+    {
+        return $this->eq(implode('|', $vals));
+    }
+}
diff --git a/Payload/BillingCharge.php b/Payload/BillingCharge.php
index 913a7c9..ac4204e 100644
--- a/Payload/BillingCharge.php
+++ b/Payload/BillingCharge.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class BillingCharge extends ARMObject {
-    public static $spec = array('object'=>'billing_charge');
+class BillingCharge extends ARMObject
+{
+    public static $spec = ['object'=>'billing_charge'];
 }
-?>
diff --git a/Payload/BillingItem.php b/Payload/BillingItem.php
index 688fb59..1c30dda 100644
--- a/Payload/BillingItem.php
+++ b/Payload/BillingItem.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class BillingItem extends ARMObject {
-    public static $spec = array('object'=>'billing_item');
+class BillingItem extends ARMObject
+{
+    public static $spec = ['object'=>'billing_item'];
 }
-?>
diff --git a/Payload/BillingSchedule.php b/Payload/BillingSchedule.php
index 1042b42..72a42e0 100644
--- a/Payload/BillingSchedule.php
+++ b/Payload/BillingSchedule.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class BillingSchedule extends ARMObject {
-    public static $spec = array('object'=>'billing_schedule');
+class BillingSchedule extends ARMObject
+{
+    public static $spec = ['object'=>'billing_schedule'];
 }
-?>
diff --git a/Payload/CheckBack.php b/Payload/CheckBack.php
index b06b9dc..5baf4ad 100644
--- a/Payload/CheckBack.php
+++ b/Payload/CheckBack.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class CheckBack extends ARMObject {
-    public static $spec = array('object'=>'check_back');
+class CheckBack extends ARMObject
+{
+    public static $spec = ['object'=>'check_back'];
 }
-?>
diff --git a/Payload/CheckFront.php b/Payload/CheckFront.php
index 053553c..7ef53cc 100644
--- a/Payload/CheckFront.php
+++ b/Payload/CheckFront.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class CheckFront extends ARMObject {
-    public static $spec = array('object'=>'check_front');
+class CheckFront extends ARMObject
+{
+    public static $spec = ['object'=>'check_front'];
 }
-?>
diff --git a/Payload/ClientToken.php b/Payload/ClientToken.php
index 257ed94..b411fd9 100644
--- a/Payload/ClientToken.php
+++ b/Payload/ClientToken.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class ClientToken extends ARMObject {
-    public static $spec = array('object'=>'access_token', 'polymorphic_type'=>'client');
+class ClientToken extends ARMObject
+{
+    public static $spec = ['object'=>'access_token', 'polymorphic_type'=>'client'];
 }
-?>
diff --git a/Payload/Customer.php b/Payload/Customer.php
index 8a2bc48..662506f 100644
--- a/Payload/Customer.php
+++ b/Payload/Customer.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Customer extends ARMObject {
-    public static $spec = array('object'=>'customer');
+class Customer extends ARMObject
+{
+    public static $spec = ['object'=>'customer'];
 }
-?>
diff --git a/Payload/Entity.php b/Payload/Entity.php
index c34d612..c9f4dfd 100644
--- a/Payload/Entity.php
+++ b/Payload/Entity.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Entity extends ARMObject {
-    public static $spec = array('object'=>'entity');
+class Entity extends ARMObject
+{
+    public static $spec = ['object'=>'entity', 'endpoint'=>'/entities'];
 }
-?>
diff --git a/Payload/Exceptions.php b/Payload/Exceptions.php
index c840782..053485d 100644
--- a/Payload/Exceptions.php
+++ b/Payload/Exceptions.php
@@ -10,4 +10,3 @@
 require(dirname(__FILE__) . '/Exceptions/TooManyRequests.php');
 require(dirname(__FILE__) . '/Exceptions/Unauthorized.php');
 require(dirname(__FILE__) . '/Exceptions/UnknownResponse.php');
-?>
diff --git a/Payload/Exceptions/BadRequest.php b/Payload/Exceptions/BadRequest.php
index 3d102df..307cd2a 100644
--- a/Payload/Exceptions/BadRequest.php
+++ b/Payload/Exceptions/BadRequest.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class BadRequest extends PayloadError {
-	public static $status_code = 400;
+class BadRequest extends PayloadError
+{
+    public static $status_code = 400;
 }
-?>
diff --git a/Payload/Exceptions/InternalServerError.php b/Payload/Exceptions/InternalServerError.php
index 13a364f..8328d0b 100644
--- a/Payload/Exceptions/InternalServerError.php
+++ b/Payload/Exceptions/InternalServerError.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class InternalServerError extends PayloadError {
-	public static $status_code = 500;
+class InternalServerError extends PayloadError
+{
+    public static $status_code = 500;
 }
-?>
diff --git a/Payload/Exceptions/InvalidAttributes.php b/Payload/Exceptions/InvalidAttributes.php
index 4e42c13..651823e 100644
--- a/Payload/Exceptions/InvalidAttributes.php
+++ b/Payload/Exceptions/InvalidAttributes.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class InvalidAttributes extends PayloadError {
-	public static $status_code = 400;
+class InvalidAttributes extends PayloadError
+{
+    public static $status_code = 400;
 }
-?>
diff --git a/Payload/Exceptions/NotFound.php b/Payload/Exceptions/NotFound.php
index d4d6480..407c3ee 100644
--- a/Payload/Exceptions/NotFound.php
+++ b/Payload/Exceptions/NotFound.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class NotFound extends PayloadError {
-	public static $status_code = 404;
+class NotFound extends PayloadError
+{
+    public static $status_code = 404;
 }
-?>
diff --git a/Payload/Exceptions/NotPermitted.php b/Payload/Exceptions/NotPermitted.php
index fbfd0f5..67319e2 100644
--- a/Payload/Exceptions/NotPermitted.php
+++ b/Payload/Exceptions/NotPermitted.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class NotPermitted extends PayloadError {
-	public static $status_code = 403;
+class NotPermitted extends PayloadError
+{
+    public static $status_code = 403;
 }
-?>
diff --git a/Payload/Exceptions/PayloadError.php b/Payload/Exceptions/PayloadError.php
index 7f08e67..9db4295 100644
--- a/Payload/Exceptions/PayloadError.php
+++ b/Payload/Exceptions/PayloadError.php
@@ -1,18 +1,20 @@
 <?php
 namespace Payload\Exceptions;
 
-class PayloadError extends \Exception {
+class PayloadError extends \Exception
+{
     public static $status_code = null;
     public $details = null;
-    public static function getClassName() {
+    public static function getClassName()
+    {
         return (new \ReflectionClass(static::class))->getShortName();
     }
 
-    public function __construct($message=null, $error = null) {
-        if ( $error && array_key_exists("details", $error) )
+    public function __construct($message = null, $error = null)
+    {
+        if ($error && array_key_exists("details", $error)) {
             $this->details = $error["details"];
+        }
         return parent::__construct($message);
-
     }
 }
-?>
diff --git a/Payload/Exceptions/ServiceUnavailable.php b/Payload/Exceptions/ServiceUnavailable.php
index 105c9fe..6904cee 100644
--- a/Payload/Exceptions/ServiceUnavailable.php
+++ b/Payload/Exceptions/ServiceUnavailable.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class ServiceUnavailable extends PayloadError {
-	public static $status_code = 503;
+class ServiceUnavailable extends PayloadError
+{
+    public static $status_code = 503;
 }
-?>
diff --git a/Payload/Exceptions/TooManyRequests.php b/Payload/Exceptions/TooManyRequests.php
index 71c891c..18fe86b 100644
--- a/Payload/Exceptions/TooManyRequests.php
+++ b/Payload/Exceptions/TooManyRequests.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class TooManyRequests extends PayloadError {
-	public static $status_code = 429;
+class TooManyRequests extends PayloadError
+{
+    public static $status_code = 429;
 }
-?>
diff --git a/Payload/Exceptions/TransactionDeclined.php b/Payload/Exceptions/TransactionDeclined.php
index bb63e18..f2217e8 100644
--- a/Payload/Exceptions/TransactionDeclined.php
+++ b/Payload/Exceptions/TransactionDeclined.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class TransactionDeclined extends PayloadError {
-	public static $status_code = 400;
+class TransactionDeclined extends PayloadError
+{
+    public static $status_code = 400;
 }
-?>
diff --git a/Payload/Exceptions/Unauthorized.php b/Payload/Exceptions/Unauthorized.php
index 5ae4762..6da7117 100644
--- a/Payload/Exceptions/Unauthorized.php
+++ b/Payload/Exceptions/Unauthorized.php
@@ -1,7 +1,7 @@
 <?php
 namespace Payload\Exceptions;
 
-class Unauthorized extends PayloadError {
-	public static $status_code = 401;
+class Unauthorized extends PayloadError
+{
+    public static $status_code = 401;
 }
-?>
diff --git a/Payload/Exceptions/UnknownResponse.php b/Payload/Exceptions/UnknownResponse.php
index bc8c14a..f0b2ddc 100644
--- a/Payload/Exceptions/UnknownResponse.php
+++ b/Payload/Exceptions/UnknownResponse.php
@@ -1,6 +1,6 @@
 <?php
 namespace Payload\Exceptions;
 
-class UnknownResponse extends PayloadError {
+class UnknownResponse extends PayloadError
+{
 }
-?>
diff --git a/Payload/Intent.php b/Payload/Intent.php
index 41d06e6..65306c1 100644
--- a/Payload/Intent.php
+++ b/Payload/Intent.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Intent extends ARMObject {
-    public static $spec = array('object'=>'intent');
+class Intent extends ARMObject
+{
+    public static $spec = ['object'=>'intent'];
 }
-?>
diff --git a/Payload/Invoice.php b/Payload/Invoice.php
index ca4326c..e33cdb4 100644
--- a/Payload/Invoice.php
+++ b/Payload/Invoice.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Invoice extends ARMObject {
-    public static $spec = array('object'=>'invoice');
+class Invoice extends ARMObject
+{
+    public static $spec = ['object'=>'invoice'];
 }
-?>
diff --git a/Payload/InvoiceAttachment.php b/Payload/InvoiceAttachment.php
new file mode 100644
index 0000000..b678cca
--- /dev/null
+++ b/Payload/InvoiceAttachment.php
@@ -0,0 +1,9 @@
+<?php
+namespace Payload;
+
+require_once('ARMObject.php');
+
+class InvoiceAttachment extends ARMObject
+{
+    public static $spec = ['object'=>'invoice_attachment'];
+}
diff --git a/Payload/InvoiceItem.php b/Payload/InvoiceItem.php
index d4f1101..98e99aa 100644
--- a/Payload/InvoiceItem.php
+++ b/Payload/InvoiceItem.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class InvoiceItem extends ARMObject {
-    public static $spec = array('object'=>'invoice_item');
+class InvoiceItem extends ARMObject
+{
+    public static $spec = ['object'=>'invoice_item'];
 }
-?>
diff --git a/Payload/Ledger.php b/Payload/Ledger.php
index 5ea2304..c1ec767 100644
--- a/Payload/Ledger.php
+++ b/Payload/Ledger.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Ledger extends ARMObject {
-    public static $spec = array('object'=>'ledger');
+class Ledger extends ARMObject
+{
+    public static $spec = ['object'=>'ledger'];
 }
-?>
diff --git a/Payload/LineItem.php b/Payload/LineItem.php
index 1f36c54..00443e4 100644
--- a/Payload/LineItem.php
+++ b/Payload/LineItem.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class LineItem extends ARMObject {
-    public static $spec = array('object'=>'line_item');
+class LineItem extends ARMObject
+{
+    public static $spec = ['object'=>'line_item'];
 }
-?>
diff --git a/Payload/OAuthToken.php b/Payload/OAuthToken.php
index 4e5840d..b7c7c64 100644
--- a/Payload/OAuthToken.php
+++ b/Payload/OAuthToken.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class OAuthToken extends ARMObject {
-    public static $spec = array('object'=>'oauth_token', 'endpoint'=>'/oauth/token');
+class OAuthToken extends ARMObject
+{
+    public static $spec = ['object'=>'oauth_token', 'endpoint'=>'/oauth/token'];
 }
-?>
diff --git a/Payload/Org.php b/Payload/Org.php
index 6468e9f..079a884 100644
--- a/Payload/Org.php
+++ b/Payload/Org.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Org extends ARMObject {
-    public static $spec = array('object'=>'org', 'endpoint'=>'/accounts/orgs');
+class Org extends ARMObject
+{
+    public static $spec = ['object'=>'org', 'endpoint'=>'/accounts/orgs'];
 }
-?>
diff --git a/Payload/PaymentActivation.php b/Payload/PaymentActivation.php
index 9fef072..154ff37 100644
--- a/Payload/PaymentActivation.php
+++ b/Payload/PaymentActivation.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class PaymentActivation extends ARMObject {
-    public static $spec = array('object'=>'payment_activation');
+class PaymentActivation extends ARMObject
+{
+    public static $spec = ['object'=>'payment_activation'];
 }
-?>
diff --git a/Payload/PaymentAllocation.php b/Payload/PaymentAllocation.php
index 060bbe9..030dbb3 100644
--- a/Payload/PaymentAllocation.php
+++ b/Payload/PaymentAllocation.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class PaymentAllocation extends ARMObject {
-    public static $spec = array('object'=>'payment_allocation');
+class PaymentAllocation extends ARMObject
+{
+    public static $spec = ['object'=>'payment_allocation'];
 }
-?>
diff --git a/Payload/PaymentLink.php b/Payload/PaymentLink.php
index 1cf7a7a..31bfa62 100644
--- a/Payload/PaymentLink.php
+++ b/Payload/PaymentLink.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class PaymentLink extends ARMObject {
-    public static $spec = array('object'=>'payment_link');
+class PaymentLink extends ARMObject
+{
+    public static $spec = ['object'=>'payment_link'];
 }
-?>
diff --git a/Payload/PaymentMethod.php b/Payload/PaymentMethod.php
index 8920180..688c870 100644
--- a/Payload/PaymentMethod.php
+++ b/Payload/PaymentMethod.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class PaymentMethod extends ARMObject {
-    public static $spec = array('object'=>'payment_method');
+class PaymentMethod extends ARMObject
+{
+    public static $spec = ['object'=>'payment_method'];
 }
-?>
diff --git a/Payload/ProcessingAccount.php b/Payload/ProcessingAccount.php
index 33b5d5b..56a398b 100644
--- a/Payload/ProcessingAccount.php
+++ b/Payload/ProcessingAccount.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class ProcessingAccount extends ARMObject {
-    public static $spec = array('object'=>'processing_account');
+class ProcessingAccount extends ARMObject
+{
+    public static $spec = ['object'=>'processing_account'];
 }
-?>
diff --git a/Payload/ProcessingAgreement.php b/Payload/ProcessingAgreement.php
index 555eaae..d2b7ce6 100644
--- a/Payload/ProcessingAgreement.php
+++ b/Payload/ProcessingAgreement.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class ProcessingAgreement extends ARMObject {
-    public static $spec = array('object'=>'processing_agreement');
+class ProcessingAgreement extends ARMObject
+{
+    public static $spec = ['object'=>'processing_agreement'];
 }
-?>
diff --git a/Payload/ProcessingRule.php b/Payload/ProcessingRule.php
index 0abce05..b25e1fe 100644
--- a/Payload/ProcessingRule.php
+++ b/Payload/ProcessingRule.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class ProcessingRule extends ARMObject {
-    public static $spec = array('object'=>'processing_rule');
+class ProcessingRule extends ARMObject
+{
+    public static $spec = ['object'=>'processing_rule'];
 }
-?>
diff --git a/Payload/ProcessingSettings.php b/Payload/ProcessingSettings.php
index ca515d8..c703cd4 100644
--- a/Payload/ProcessingSettings.php
+++ b/Payload/ProcessingSettings.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class ProcessingSettings extends ARMObject {
-    public static $spec = array('object'=>'processing_settings');
+class ProcessingSettings extends ARMObject
+{
+    public static $spec = ['object'=>'processing_settings'];
 }
-?>
diff --git a/Payload/Profile.php b/Payload/Profile.php
index 0a27719..4a1dae1 100644
--- a/Payload/Profile.php
+++ b/Payload/Profile.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Profile extends ARMObject {
-    public static $spec = array('object'=>'profile');
+class Profile extends ARMObject
+{
+    public static $spec = ['object'=>'profile'];
 }
-?>
diff --git a/Payload/Stakeholder.php b/Payload/Stakeholder.php
index 219ab64..a903a49 100644
--- a/Payload/Stakeholder.php
+++ b/Payload/Stakeholder.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Stakeholder extends ARMObject {
-    public static $spec = array('object'=>'stakeholder');
+class Stakeholder extends ARMObject
+{
+    public static $spec = ['object'=>'stakeholder'];
 }
-?>
diff --git a/Payload/Transaction.php b/Payload/Transaction.php
index a0a2114..60e90fa 100644
--- a/Payload/Transaction.php
+++ b/Payload/Transaction.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Transaction extends ARMObject {
-    public static $spec = array('object'=>'transaction');
+class Transaction extends ARMObject
+{
+    public static $spec = ['object'=>'transaction'];
 }
-?>
diff --git a/Payload/TransactionOperation.php b/Payload/TransactionOperation.php
index 22e62e8..ea80333 100644
--- a/Payload/TransactionOperation.php
+++ b/Payload/TransactionOperation.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class TransactionOperation extends ARMObject {
-    public static $spec = array('object'=>'transaction_operation');
+class TransactionOperation extends ARMObject
+{
+    public static $spec = ['object'=>'transaction_operation'];
 }
-?>
diff --git a/Payload/Transfer.php b/Payload/Transfer.php
index 879bb64..6020222 100644
--- a/Payload/Transfer.php
+++ b/Payload/Transfer.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Transfer extends ARMObject {
-    public static $spec = array('object'=>'transfer');
+class Transfer extends ARMObject
+{
+    public static $spec = ['object'=>'transfer'];
 }
-?>
diff --git a/Payload/User.php b/Payload/User.php
index 2f707b7..2ab50f2 100644
--- a/Payload/User.php
+++ b/Payload/User.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class User extends ARMObject {
-    public static $spec = array('object'=>'user');
+class User extends ARMObject
+{
+    public static $spec = ['object'=>'user'];
 }
-?>
diff --git a/Payload/Utils.php b/Payload/Utils.php
index e7d0596..d0dc0ab 100644
--- a/Payload/Utils.php
+++ b/Payload/Utils.php
@@ -1,49 +1,42 @@
 <?php
 namespace Payload;
 
-class Utils {
-    public static function subclasses($parent) {
-        $result = array();
-        foreach (get_declared_classes() as $class) {
-            if (is_subclass_of($class, $parent))
-                $result[] = $class;
-        }
-        return $result;
-    }
-
-    public static function is_assoc_array($arr) {
+class Utils
+{
+    public static function is_assoc_array($arr)
+    {
         return is_array($arr) && array_keys($arr) !== range(0, count($arr) - 1);
     }
 
-    public static function data2object($data) {
-        $object = array();
-        foreach ( $data as $key => $val ) {
+    public static function data2object($data)
+    {
+        $registry = ARMObject::getRegistry();
+        $object = [];
+        foreach ($data as $key => $val) {
             $object[$key] = $val;
-            if ( Utils::is_assoc_array($val) && isset($val['object']) ) {
-                foreach (Utils::subclasses(ARMObject::class) as $cls) {
-                    if ($cls::$spec['object'] == $val['object']) {
-                        $object[$key] = $cls::new($val);
-                        break;
-                    }
+            if (Utils::is_assoc_array($val) && isset($val['object'])) {
+                if (isset($registry[$val['object']])) {
+                    $cls = $registry[$val['object']];
+                    $object[$key] = $cls::new($val);
                 }
-            } else if (is_array($val)) {
+            } elseif (is_array($val)) {
                 $object[$key] = self::data2object($val);
             }
         }
         return $object;
     }
 
-    public static function object2data($object) {
-        $data = array();
-        foreach ( $object as $key => $val ) {
+    public static function object2data($object)
+    {
+        $data = [];
+        foreach ($object as $key => $val) {
             $data[$key] = $val;
-            if ( $val instanceof ARMObject ) {
+            if ($val instanceof ARMObject) {
                 $data[$key] = $val->data();
-            } else if (is_array($val)) {
+            } elseif (is_array($val)) {
                 $data[$key] = self::object2data($val);
             }
         }
         return $data;
     }
 }
-?>
diff --git a/Payload/Webhook.php b/Payload/Webhook.php
index 47aa8b5..a0c62e3 100644
--- a/Payload/Webhook.php
+++ b/Payload/Webhook.php
@@ -3,7 +3,7 @@
 
 require_once('ARMObject.php');
 
-class Webhook extends ARMObject {
-    public static $spec = array('object'=>'webhook');
+class Webhook extends ARMObject
+{
+    public static $spec = ['object'=>'webhook'];
 }
-?>
diff --git a/Payload/WebhookLog.php b/Payload/WebhookLog.php
new file mode 100644
index 0000000..985baee
--- /dev/null
+++ b/Payload/WebhookLog.php
@@ -0,0 +1,9 @@
+<?php
+namespace Payload;
+
+require_once('ARMObject.php');
+
+class WebhookLog extends ARMObject
+{
+    public static $spec = ['object'=>'webhook_log'];
+}
diff --git a/Tests/AccountTest.php b/Tests/Int/AccountTest.php
similarity index 100%
rename from Tests/AccountTest.php
rename to Tests/Int/AccountTest.php
diff --git a/Tests/BillingTest.php b/Tests/Int/BillingTest.php
similarity index 100%
rename from Tests/BillingTest.php
rename to Tests/Int/BillingTest.php
diff --git a/Tests/Fixtures.php b/Tests/Int/Fixtures.php
similarity index 100%
rename from Tests/Fixtures.php
rename to Tests/Int/Fixtures.php
diff --git a/Tests/InvoiceTest.php b/Tests/Int/InvoiceTest.php
similarity index 100%
rename from Tests/InvoiceTest.php
rename to Tests/Int/InvoiceTest.php
diff --git a/Tests/PaymentLinkTest.php b/Tests/Int/PaymentLinkTest.php
similarity index 100%
rename from Tests/PaymentLinkTest.php
rename to Tests/Int/PaymentLinkTest.php
diff --git a/Tests/PaymentTest.php b/Tests/Int/PaymentTest.php
similarity index 100%
rename from Tests/PaymentTest.php
rename to Tests/Int/PaymentTest.php
diff --git a/Tests/TransactionTest.php b/Tests/Int/TransactionTest.php
similarity index 100%
rename from Tests/TransactionTest.php
rename to Tests/Int/TransactionTest.php
diff --git a/Tests/ARMRequestTest.php b/Tests/Unit/ARMRequestTest.php
similarity index 100%
rename from Tests/ARMRequestTest.php
rename to Tests/Unit/ARMRequestTest.php
diff --git a/Tests/Unit/AttrTest.php b/Tests/Unit/AttrTest.php
new file mode 100644
index 0000000..0f83031
--- /dev/null
+++ b/Tests/Unit/AttrTest.php
@@ -0,0 +1,183 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use Payload\Attr;
+
+final class AttrTest extends TestCase
+{
+    // --- Constructor and key building ---
+
+    public function test_constructor_with_param_only()
+    {
+        $attr = new Attr('status');
+        $this->assertEquals('status', strval($attr));
+    }
+
+    public function test_constructor_with_null_param()
+    {
+        $attr = new Attr();
+        $this->assertEquals('', strval($attr));
+    }
+
+    public function test_nested_key_via_parent()
+    {
+        $parent = new Attr('customer');
+        $child = new Attr('name', $parent);
+        $this->assertEquals('customer[name]', strval($child));
+    }
+
+    public function test_deeply_nested_key()
+    {
+        $root = new Attr('customer');
+        $mid = new Attr('address', $root);
+        $leaf = new Attr('city', $mid);
+        $this->assertEquals('customer[address][city]', strval($leaf));
+    }
+
+    // --- __get magic method ---
+
+    public function test_get_creates_nested_attr()
+    {
+        $attr = new Attr('customer');
+        $nested = $attr->name;
+        $this->assertInstanceOf(Attr::class, $nested);
+        $this->assertEquals('customer[name]', strval($nested));
+    }
+
+    public function test_get_chained_multiple_levels()
+    {
+        $attr = new Attr('customer');
+        $deep = $attr->address->city;
+        $this->assertEquals('customer[address][city]', strval($deep));
+    }
+
+    // --- eq ---
+
+    public function test_eq_returns_filter_array()
+    {
+        $attr = new Attr('status');
+        $result = $attr->eq('active');
+        $this->assertEquals(['status' => 'active'], $result);
+    }
+
+    public function test_eq_with_nested_key()
+    {
+        $attr = new Attr('customer');
+        $result = $attr->name->eq('John');
+        $this->assertEquals(['customer[name]' => 'John'], $result);
+    }
+
+    public function test_eq_with_numeric_value()
+    {
+        $attr = new Attr('amount');
+        $result = $attr->eq(100);
+        $this->assertEquals(['amount' => 100], $result);
+    }
+
+    // --- ne ---
+
+    public function test_ne_prepends_exclamation()
+    {
+        $attr = new Attr('status');
+        $result = $attr->ne('inactive');
+        $this->assertEquals(['status' => '!inactive'], $result);
+    }
+
+    // --- lt ---
+
+    public function test_lt_prepends_less_than()
+    {
+        $attr = new Attr('amount');
+        $result = $attr->lt(100);
+        $this->assertEquals(['amount' => '<100'], $result);
+    }
+
+    // --- le ---
+
+    public function test_le_prepends_less_than_or_equal()
+    {
+        $attr = new Attr('amount');
+        $result = $attr->le(100);
+        $this->assertEquals(['amount' => '<=100'], $result);
+    }
+
+    // --- gt ---
+
+    public function test_gt_prepends_greater_than()
+    {
+        $attr = new Attr('amount');
+        $result = $attr->gt(50);
+        $this->assertEquals(['amount' => '>50'], $result);
+    }
+
+    // --- ge ---
+
+    public function test_ge_prepends_greater_than_or_equal()
+    {
+        $attr = new Attr('amount');
+        $result = $attr->ge(50);
+        $this->assertEquals(['amount' => '>=50'], $result);
+    }
+
+    // --- contains ---
+
+    public function test_contains_wraps_with_wildcards()
+    {
+        $attr = new Attr('name');
+        $result = $attr->contains('john');
+        $this->assertEquals(['name' => '?*john*'], $result);
+    }
+
+    // --- in ---
+
+    public function test_in_joins_values_with_pipe()
+    {
+        $attr = new Attr('status');
+        $result = $attr->in('active', 'pending');
+        $this->assertEquals(['status' => 'active|pending'], $result);
+    }
+
+    public function test_in_single_value()
+    {
+        $attr = new Attr('status');
+        $result = $attr->in('active');
+        $this->assertEquals(['status' => 'active'], $result);
+    }
+
+    public function test_in_multiple_values()
+    {
+        $attr = new Attr('status');
+        $result = $attr->in('active', 'pending', 'closed');
+        $this->assertEquals(['status' => 'active|pending|closed'], $result);
+    }
+
+    // --- Comparison methods with nested keys ---
+
+    public function test_ne_with_nested_key()
+    {
+        $attr = new Attr('customer');
+        $result = $attr->status->ne('inactive');
+        $this->assertEquals(['customer[status]' => '!inactive'], $result);
+    }
+
+    public function test_gt_with_nested_key()
+    {
+        $attr = new Attr('order');
+        $result = $attr->total->gt(200);
+        $this->assertEquals(['order[total]' => '>200'], $result);
+    }
+
+    public function test_contains_with_nested_key()
+    {
+        $attr = new Attr('customer');
+        $result = $attr->email->contains('example');
+        $this->assertEquals(['customer[email]' => '?*example*'], $result);
+    }
+
+    public function test_in_with_nested_key()
+    {
+        $attr = new Attr('customer');
+        $result = $attr->type->in('business', 'individual');
+        $this->assertEquals(['customer[type]' => 'business|individual'], $result);
+    }
+}
diff --git a/Tests/Unit/QueryParamsTest.php b/Tests/Unit/QueryParamsTest.php
new file mode 100644
index 0000000..df77fbc
--- /dev/null
+++ b/Tests/Unit/QueryParamsTest.php
@@ -0,0 +1,247 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use Payload\API as pl;
+use phpmock\phpunit\PHPMock;
+
+final class QueryParamsTest extends TestCase
+{
+    use PHPMock;
+
+    protected $original_api_version;
+    protected $original_api_key;
+    protected $original_api_url;
+    protected $curl_requests = [];
+
+    protected function setUp(): void
+    {
+        $this->original_api_version = Payload\API::$api_version ?? null;
+        $this->original_api_key = Payload\API::$api_key ?? null;
+        $this->original_api_url = Payload\API::$api_url ?? null;
+
+        Payload\API::$api_key = 'test_key';
+        Payload\API::$api_url = 'https://api.test.com';
+        Payload\API::$api_version = null;
+
+        $this->curl_requests = [];
+        $this->mockCurlFunctions();
+    }
+
+    protected function tearDown(): void
+    {
+        Payload\API::$api_version = $this->original_api_version;
+        Payload\API::$api_key = $this->original_api_key;
+        Payload\API::$api_url = $this->original_api_url;
+    }
+
+    protected function mockCurlFunctions()
+    {
+        $test = $this;
+
+        $curl_init = $this->getFunctionMock('Payload', 'curl_init');
+        $curl_init->expects($this->any())->willReturnCallback(function ($url) use ($test) {
+            $handle = 'mock_handle_' . count($test->curl_requests);
+            $test->curl_requests[$handle] = [
+                'url' => $url,
+                'options' => [],
+            ];
+            return $handle;
+        });
+
+        $curl_setopt = $this->getFunctionMock('Payload', 'curl_setopt');
+        $curl_setopt->expects($this->any())->willReturnCallback(function ($handle, $option, $value) use ($test) {
+            if (!isset($test->curl_requests[$handle])) {
+                $test->curl_requests[$handle] = ['options' => []];
+            }
+            $test->curl_requests[$handle]['options'][$option] = $value;
+            return true;
+        });
+
+        $curl_exec = $this->getFunctionMock('Payload', 'curl_exec');
+        $curl_exec->expects($this->any())->willReturn(json_encode([
+            'object' => 'list',
+            'values' => [
+                ['object' => 'customer', 'id' => 'cust_1', 'email' => 'a@example.com', 'name' => 'A'],
+                ['object' => 'customer', 'id' => 'cust_2', 'email' => 'b@example.com', 'name' => 'B'],
+            ],
+        ]));
+
+        $curl_getinfo = $this->getFunctionMock('Payload', 'curl_getinfo');
+        $curl_getinfo->expects($this->any())->willReturnCallback(function ($handle, $option = null) {
+            if ($option === CURLINFO_HTTP_CODE) {
+                return 200;
+            }
+            return null;
+        });
+
+        $curl_close = $this->getFunctionMock('Payload', 'curl_close');
+        $curl_close->expects($this->any())->willReturn(true);
+    }
+
+    protected function getRequestUrl()
+    {
+        $this->assertNotEmpty($this->curl_requests);
+        $handle = array_key_first($this->curl_requests);
+        return $this->curl_requests[$handle]['url'];
+    }
+
+    protected function getQueryParams()
+    {
+        $url = $this->getRequestUrl();
+        $query = parse_url($url, PHP_URL_QUERY);
+        if ($query === null) {
+            return [];
+        }
+        parse_str($query, $params);
+        return $params;
+    }
+
+    // --- order_by tests ---
+
+    public function test_order_by_on_arm_request()
+    {
+        $req = new Payload\ARMRequest(Payload\Customer::class);
+        $req->order_by('created_at')->all();
+
+        $params = $this->getQueryParams();
+        $this->assertArrayHasKey('order_by', $params);
+        $this->assertContains('created_at', (array)$params['order_by']);
+    }
+
+    public function test_order_by_on_arm_object()
+    {
+        Payload\Customer::order_by('created_at')->all();
+
+        $params = $this->getQueryParams();
+        $this->assertArrayHasKey('order_by', $params);
+        $this->assertContains('created_at', (array)$params['order_by']);
+    }
+
+    public function test_order_by_multiple_fields()
+    {
+        Payload\Customer::order_by('created_at', 'name')->all();
+
+        $params = $this->getQueryParams();
+        $this->assertArrayHasKey('order_by', $params);
+        $order_by = (array)$params['order_by'];
+        $this->assertContains('created_at', $order_by);
+        $this->assertContains('name', $order_by);
+    }
+
+    // --- limit tests ---
+
+    public function test_limit_on_arm_request()
+    {
+        $req = new Payload\ARMRequest(Payload\Customer::class);
+        $req->limit(10)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertArrayHasKey('limit', $params);
+        $this->assertEquals(10, $params['limit']);
+    }
+
+    public function test_limit_on_arm_object()
+    {
+        Payload\Customer::limit(5)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertArrayHasKey('limit', $params);
+        $this->assertEquals(5, $params['limit']);
+    }
+
+    // --- offset tests ---
+
+    public function test_offset_on_arm_request()
+    {
+        $req = new Payload\ARMRequest(Payload\Customer::class);
+        $req->offset(20)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertArrayHasKey('offset', $params);
+        $this->assertEquals(20, $params['offset']);
+    }
+
+    public function test_offset_on_arm_object()
+    {
+        Payload\Customer::offset(15)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertArrayHasKey('offset', $params);
+        $this->assertEquals(15, $params['offset']);
+    }
+
+    // --- chaining tests ---
+
+    public function test_limit_and_offset_chained()
+    {
+        Payload\Customer::limit(10)->offset(20)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertEquals(10, $params['limit']);
+        $this->assertEquals(20, $params['offset']);
+    }
+
+    public function test_order_by_with_limit_and_offset()
+    {
+        Payload\Customer::order_by('created_at')->limit(5)->offset(10)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertContains('created_at', (array)$params['order_by']);
+        $this->assertEquals(5, $params['limit']);
+        $this->assertEquals(10, $params['offset']);
+    }
+
+    public function test_filter_by_with_order_by_limit_offset()
+    {
+        Payload\Customer::filter_by(
+            ['status' => 'active']
+        )->order_by('created_at')->limit(25)->offset(50)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertEquals('active', $params['status']);
+        $this->assertContains('created_at', (array)$params['order_by']);
+        $this->assertEquals(25, $params['limit']);
+        $this->assertEquals(50, $params['offset']);
+    }
+
+    // --- default_params tests ---
+
+    public function test_default_params_applied()
+    {
+        $original = Payload\Customer::getDefaultParams();
+        Payload\Customer::setDefaultParams(['limit' => 100]);
+        $this->assertEquals([], Payload\Account::getDefaultParams());
+
+        Payload\Customer::filter_by(['status' => 'active'])->all();
+
+        $params = $this->getQueryParams();
+        $this->assertEquals(100, $params['limit']);
+
+        Payload\Customer::setDefaultParams($original);
+    }
+
+    public function test_default_params_do_not_override_explicit()
+    {
+        $original = Payload\Customer::getDefaultParams();
+        Payload\Customer::setDefaultParams(['limit' => 100]);
+
+        Payload\Customer::limit(5)->all();
+
+        $params = $this->getQueryParams();
+        $this->assertEquals(5, $params['limit']);
+
+        Payload\Customer::setDefaultParams($original);
+    }
+
+    // --- no params when not set ---
+
+    public function test_no_query_params_when_none_set()
+    {
+        Payload\Customer::filter_by([])->all();
+
+        $url = $this->getRequestUrl();
+        $this->assertStringNotContainsString('order_by', $url);
+        $this->assertStringNotContainsString('limit', $url);
+        $this->assertStringNotContainsString('offset', $url);
+    }
+}
diff --git a/composer.json b/composer.json
index d8b0a73..7ac8ed7 100644
--- a/composer.json
+++ b/composer.json
@@ -21,7 +21,7 @@
   },
   "minimum-stability": "stable",
   "prefer-stable": true,
-  "version": "0.4.0",
+  "version": "1.0.0",
   "autoload": {
     "psr-4": {
       "Payload\\": "Payload/"
diff --git a/import.php b/import.php
index c5483cc..2adb56a 100644
--- a/import.php
+++ b/import.php
@@ -13,7 +13,9 @@
 require(dirname(__FILE__) . '/Payload/BillingSchedule.php');
 require(dirname(__FILE__) . '/Payload/BillingCharge.php');
 require(dirname(__FILE__) . '/Payload/LineItem.php');
+require(dirname(__FILE__) . '/Payload/Ledger.php');
 require(dirname(__FILE__) . '/Payload/Webhook.php');
+require(dirname(__FILE__) . '/Payload/WebhookLog.php');
 require(dirname(__FILE__) . '/Payload/PaymentActivation.php');
 require(dirname(__FILE__) . '/Payload/AccessToken.php');
 require(dirname(__FILE__) . '/Payload/ClientToken.php');
@@ -22,6 +24,7 @@
 require(dirname(__FILE__) . '/Payload/BillingItem.php');
 require(dirname(__FILE__) . '/Payload/Intent.php');
 require(dirname(__FILE__) . '/Payload/InvoiceItem.php');
+require(dirname(__FILE__) . '/Payload/InvoiceAttachment.php');
 require(dirname(__FILE__) . '/Payload/PaymentAllocation.php');
 require(dirname(__FILE__) . '/Payload/Entity.php');
 require(dirname(__FILE__) . '/Payload/Stakeholder.php');