diff --git a/src/Endpoints/AbstractRequest.php b/src/Endpoints/AbstractRequest.php
index be90c3e..8303a52 100644
--- a/src/Endpoints/AbstractRequest.php
+++ b/src/Endpoints/AbstractRequest.php
@@ -57,6 +57,7 @@ public function send()
 
     abstract public function toArray(): array;
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->toArray();
diff --git a/src/Models/AbstractHolder.php b/src/Models/AbstractHolder.php
index 4cd0edf..beb9aee 100644
--- a/src/Models/AbstractHolder.php
+++ b/src/Models/AbstractHolder.php
@@ -52,6 +52,7 @@ public function toArray(): array
     /**
      * @return TEntry[]
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->toArray();
diff --git a/src/Models/Contact.php b/src/Models/Contact.php
index 01f730e..543630f 100644
--- a/src/Models/Contact.php
+++ b/src/Models/Contact.php
@@ -427,6 +427,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());
diff --git a/src/Models/ContactListStatus.php b/src/Models/ContactListStatus.php
index e11804f..adb00dc 100644
--- a/src/Models/ContactListStatus.php
+++ b/src/Models/ContactListStatus.php
@@ -73,6 +73,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());
diff --git a/src/Models/Contactlist.php b/src/Models/Contactlist.php
index d70f5b1..b17db76 100644
--- a/src/Models/Contactlist.php
+++ b/src/Models/Contactlist.php
@@ -214,6 +214,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());
diff --git a/src/Models/CustomFieldDefinition.php b/src/Models/CustomFieldDefinition.php
index 6de81cf..0475097 100644
--- a/src/Models/CustomFieldDefinition.php
+++ b/src/Models/CustomFieldDefinition.php
@@ -148,6 +148,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());
diff --git a/src/Models/CustomFieldOption.php b/src/Models/CustomFieldOption.php
index c1459ef..b05fda7 100644
--- a/src/Models/CustomFieldOption.php
+++ b/src/Models/CustomFieldOption.php
@@ -108,6 +108,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());
diff --git a/src/Models/CustomFieldValue.php b/src/Models/CustomFieldValue.php
index 7e7cf41..801a64c 100644
--- a/src/Models/CustomFieldValue.php
+++ b/src/Models/CustomFieldValue.php
@@ -104,6 +104,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());
diff --git a/src/Models/Model.php b/src/Models/Model.php
index 5f1210c..1fa9b94 100644
--- a/src/Models/Model.php
+++ b/src/Models/Model.php
@@ -37,6 +37,7 @@ public static function fromJSON(\stdClass $json): object
      */
     abstract public function toArray(): array;
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->toArray();
diff --git a/src/Models/Order.php b/src/Models/Order.php
index 0ba9501..fc69033 100644
--- a/src/Models/Order.php
+++ b/src/Models/Order.php
@@ -182,6 +182,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());
diff --git a/tests/Endpoints/Contactlists/Search/RequestTest.php b/tests/Endpoints/Contactlists/Search/RequestTest.php
index 7af5b0a..137cdd8 100644
--- a/tests/Endpoints/Contactlists/Search/RequestTest.php
+++ b/tests/Endpoints/Contactlists/Search/RequestTest.php
@@ -29,6 +29,7 @@ public function testDefaultEndpoint(): void
 
             // The query parameters to send
             $query = $value['query'];
+            $this->assertTrue(is_array($query), 'Query must be an array');
             $this->assertArrayHasKey('limit', $query);
             $this->assertArrayHasKey('offset', $query);
             $this->assertEquals(0, $query['offset'], 'The first page should have 0 offset');
diff --git a/tests/Endpoints/Contacts/Search/RequestTest.php b/tests/Endpoints/Contacts/Search/RequestTest.php
index 7a3ca29..2eef99a 100644
--- a/tests/Endpoints/Contacts/Search/RequestTest.php
+++ b/tests/Endpoints/Contacts/Search/RequestTest.php
@@ -31,6 +31,7 @@ public function testDefaultEndpoint(): void
 
             // The query parameters to send
             $query = $value['query'];
+            $this->assertTrue(is_array($query), 'Query must be an array');
             $this->assertArrayHasKey('limit', $query);
             $this->assertArrayHasKey('offset', $query);
             $this->assertEquals(0, $query['offset'], 'The first page should have 0 offset');
@@ -57,6 +58,7 @@ public function testFilteredEndpoint(): void
 
             // The query parameters to send
             $query = $value['query'];
+            $this->assertTrue(is_array($query), 'Query must be an array');
             $this->assertArrayHasKey('limit', $query);
             $this->assertArrayHasKey('offset', $query);
             $this->assertEquals(50, $query['offset'], 'The second page should the limit value');
diff --git a/tests/Endpoints/CustomFields/Search/RequestTest.php b/tests/Endpoints/CustomFields/Search/RequestTest.php
index 651e303..a16ef8f 100644
--- a/tests/Endpoints/CustomFields/Search/RequestTest.php
+++ b/tests/Endpoints/CustomFields/Search/RequestTest.php
@@ -32,6 +32,7 @@ public function testDefaultEndpoint(): void
 
             // The query parameters to send
             $query = $value['query'];
+            $this->assertTrue(is_array($query), 'Query must be an array');
             $this->assertArrayHasKey('limit', $query);
             $this->assertArrayHasKey('offset', $query);
             $this->assertEquals(0, $query['offset'], 'The first page should have 0 offset');
@@ -58,6 +59,7 @@ public function testFilteredEndpoint(): void
 
             // The query parameters to send
             $query = $value['query'];
+            $this->assertTrue(is_array($query), 'Query must be an array');
             $this->assertArrayHasKey('limit', $query);
             $this->assertArrayHasKey('offset', $query);
             $this->assertEquals(50, $query['offset'], 'The second page should the limit value');
diff --git a/tests/Mock/ModelMock.php b/tests/Mock/ModelMock.php
index 9335f84..8f31f66 100644
--- a/tests/Mock/ModelMock.php
+++ b/tests/Mock/ModelMock.php
@@ -31,6 +31,7 @@ public function toArray(): array
         ];
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize(): array
     {
         return $this->removeEmptyValues($this->toArray());