diff --git a/Models/SurveyTemplate.php b/Models/SurveyTemplate.php
index a501b6f..af7a003 100755
--- a/Models/SurveyTemplate.php
+++ b/Models/SurveyTemplate.php
@@ -309,7 +309,7 @@ class SurveyTemplate
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/SurveyTemplateElement.php b/Models/SurveyTemplateElement.php
index e5a12ac..edf8778 100755
--- a/Models/SurveyTemplateElement.php
+++ b/Models/SurveyTemplateElement.php
@@ -190,7 +190,7 @@ class SurveyTemplateElement
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/SurveyTemplateElementL11n.php b/Models/SurveyTemplateElementL11n.php
index b6595e3..3f66788 100755
--- a/Models/SurveyTemplateElementL11n.php
+++ b/Models/SurveyTemplateElementL11n.php
@@ -149,7 +149,7 @@ class SurveyTemplateElementL11n implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/SurveyTemplateL11n.php b/Models/SurveyTemplateL11n.php
index 59e3ec8..bc193c0 100755
--- a/Models/SurveyTemplateL11n.php
+++ b/Models/SurveyTemplateL11n.php
@@ -149,7 +149,7 @@ class SurveyTemplateL11n implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }
diff --git a/Models/SurveyTemplateLabelL11n.php b/Models/SurveyTemplateLabelL11n.php
index a3ef1b8..5dac035 100755
--- a/Models/SurveyTemplateLabelL11n.php
+++ b/Models/SurveyTemplateLabelL11n.php
@@ -136,7 +136,7 @@ class SurveyTemplateLabelL11n implements \JsonSerializable, ArrayableInterface
     /**
      * {@inheritdoc}
      */
-    public function jsonSerialize()
+    public function jsonSerialize() : mixed
     {
         return $this->toArray();
     }