diff --git a/psalm.xml b/psalm.xml
index 4b6b5a8..48ab4d8 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <psalm
-    errorLevel="5"
+    errorLevel="1"
     resolveFromConfigFile="true"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
diff --git a/src/Api.php b/src/Api.php
index c4353a6..bd83a41 100644
--- a/src/Api.php
+++ b/src/Api.php
@@ -54,7 +54,9 @@ public function newRequest(string $method, string $resource, array $headers = []
 
     public function setRequest(RequestInterface $request): self
     {
-        $request = $request->withHeader('Authorization', 'Bearer ' . $this->apiKey);
+        if (!$request->hasHeader('Authorization')) {
+            $request = $request->withHeader('Authorization', 'Bearer ' . $this->apiKey);
+        }
 
         if (!$request->hasHeader('Accept')) {
             $request = $request->withHeader('Accept', 'application/json');
diff --git a/src/Clients/Traits/DocumentClientTrait.php b/src/Clients/Traits/DocumentClientTrait.php
index a958d00..7baa134 100644
--- a/src/Clients/Traits/DocumentClientTrait.php
+++ b/src/Clients/Traits/DocumentClientTrait.php
@@ -5,7 +5,6 @@
 namespace Sysix\LexOffice\Clients\Traits;
 
 use Psr\Http\Message\ResponseInterface;
-use stdClass;
 use Sysix\LexOffice\Clients\File;
 use Sysix\LexOffice\Utils;
 
@@ -25,10 +24,9 @@ public function document(string $id, bool $asContent = false, string $acceptHead
             return $response;
         }
 
-        /** @var ?stdClass{documentField: string} $content */
         $content = Utils::getJsonFromResponse($response);
 
-        if ($content === null) {
+        if ($content === null || !is_object($content) || !property_exists($content, 'documentFileId') || !is_string($content->documentFileId)) {
             return $response;
         }
 
diff --git a/src/PaginationClient.php b/src/PaginationClient.php
index 20ff384..b8e0afc 100644
--- a/src/PaginationClient.php
+++ b/src/PaginationClient.php
@@ -5,7 +5,6 @@
 namespace Sysix\LexOffice;
 
 use Psr\Http\Message\ResponseInterface;
-use stdClass;
 
 abstract class PaginationClient extends BaseClient
 {
@@ -52,10 +51,13 @@ public function getAll(): ResponseInterface
         trigger_error(self::class . '::' . __METHOD__ . ' should not be called anymore, in future versions this method WILL not exist', E_USER_DEPRECATED);
 
         $response = $this->getPage(0);
-        /** @var ?stdClass{totalPages:int, content:stdClass[]} $result */
         $result = Utils::getJsonFromResponse($response);
 
-        if ($result === null || $result->totalPages == 1) {
+        if (
+            $result === null || !is_object($result) ||
+            !property_exists($result, 'totalPages') || $result->totalPages == 1 ||
+            !property_exists($result, 'content')
+        ) {
             return $response;
         }
 
@@ -67,19 +69,19 @@ public function getAll(): ResponseInterface
                 return $responsePage;
             }
 
-            /** @var ?stdClass{totalPages:int, content:stdClass[]} $resultPage */
             $resultPage = Utils::getJsonFromResponse($responsePage);
 
-            if ($resultPage === null) {
+            if (
+                $resultPage === null ||
+                !is_object($resultPage) ||
+                !property_exists($resultPage, 'content') ||
+                !is_array($resultPage->content) ||
+                !is_array($result->content)
+            ) {
                 return $responsePage;
             }
 
-            foreach ($resultPage->content as $entity) {
-                $result->content = [
-                    ...$result->content,
-                    $entity
-                ];
-            }
+            array_push($result->content, ...$resultPage->content);
         }
 
         return $response->withBody(Utils::createStream($result));
diff --git a/src/Utils.php b/src/Utils.php
index cd5194e..35eb4ab 100644
--- a/src/Utils.php
+++ b/src/Utils.php
@@ -61,6 +61,7 @@ public static function jsonEncode(mixed $value, int $options = 0, int $depth = 5
      */
     public static function jsonDecode(string $json, bool $assoc = false, int $depth = 512, int $options = 0): mixed
     {
+        /** @var mixed $data */
         $data = json_decode($json, $assoc, $depth, $options);
         if (JSON_ERROR_NONE !== json_last_error()) {
             throw new InvalidArgumentException('json_decode error: ' . json_last_error_msg());
diff --git a/tests/PaginationClientTest.php b/tests/PaginationClientTest.php
index c898802..dcdff92 100644
--- a/tests/PaginationClientTest.php
+++ b/tests/PaginationClientTest.php
@@ -12,7 +12,7 @@
 class PaginationClientTest extends TestClient
 {
     /**
-     * @param Response[] $responses
+     * @param array<int, Response> $responses
      *
      * @return array{0: Api&MockObject, 1: PaginationClient}
      */
diff --git a/tests/TestClient.php b/tests/TestClient.php
index eb33dda..592fb42 100644
--- a/tests/TestClient.php
+++ b/tests/TestClient.php
@@ -41,7 +41,7 @@ public function createApiMockObject(Response $response)
     }
 
     /**
-     * @param Response[] $responses
+     * @param array<int, Response> $responses
      *
      * @return Api&MockObject
      */
@@ -76,8 +76,8 @@ public function createClientMockObject(string $className): array
     /**
      * @template T of ClientInterface
      *
-     * @param class-string<T> $className
-     * @param Response[]      $responses
+     * @param class-string<T>      $className
+     * @param array<int, Response> $responses
      *
      * @return array{0: Api&MockObject, 1: T&MockObject}
      */
diff --git a/tests/UtilsTest.php b/tests/UtilsTest.php
index c27f18d..e518398 100644
--- a/tests/UtilsTest.php
+++ b/tests/UtilsTest.php
@@ -36,6 +36,8 @@ public function testGetJsonFromResponseWithValidHeader(): void
         ], (string) json_encode([
             'test' => true
         ]));
+
+        /** @var object $json */
         $json = Utils::getJsonFromResponse($response);
 
         $this->assertEquals((object)[
@@ -50,6 +52,8 @@ public function testGetJsonFromResponseWithValidCharsetHeader(): void
         ], (string) json_encode([
             'test' => true
         ]));
+
+        /** @var object $json */
         $json = Utils::getJsonFromResponse($response);
 
         $this->assertEquals((object)[
@@ -59,6 +63,8 @@ public function testGetJsonFromResponseWithValidCharsetHeader(): void
 
     public function testJsonDecodeValid(): void
     {
+
+        /** @var object $json */
         $json = Utils::jsonDecode('{"content":"test","object":{"content":"test2"}}');
 
         $this->assertEquals($json, (object)[