diff --git a/Models/Client.php b/Models/Client.php
index aac8fc0..6962cae 100755
--- a/Models/Client.php
+++ b/Models/Client.php
@@ -347,7 +347,7 @@ class Client
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/ClientAttribute.php b/Models/ClientAttribute.php
index c3c36e6..aa2bbf9 100755
--- a/Models/ClientAttribute.php
+++ b/Models/ClientAttribute.php
@@ -97,7 +97,7 @@ class ClientAttribute implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/ClientAttributeType.php b/Models/ClientAttributeType.php
index 71ede2d..540b7ce 100755
--- a/Models/ClientAttributeType.php
+++ b/Models/ClientAttributeType.php
@@ -153,7 +153,7 @@ class ClientAttributeType implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/ClientAttributeTypeL11n.php b/Models/ClientAttributeTypeL11n.php
index d578a84..6b98843 100755
--- a/Models/ClientAttributeTypeL11n.php
+++ b/Models/ClientAttributeTypeL11n.php
@@ -129,7 +129,7 @@ class ClientAttributeTypeL11n implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/ClientAttributeValue.php b/Models/ClientAttributeValue.php
index de48bf7..45642de 100755
--- a/Models/ClientAttributeValue.php
+++ b/Models/ClientAttributeValue.php
@@ -248,7 +248,7 @@ class ClientAttributeValue implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }