diff --git a/src/Model/Collection.php b/src/Model/Collection.php
index fe72caa..92f5a07 100644
--- a/src/Model/Collection.php
+++ b/src/Model/Collection.php
@@ -55,6 +55,7 @@ public function count()
      * which is a value of any type other than a resource.
      * @since 5.4.0
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         if ($this->key !== null) {
@@ -62,4 +63,4 @@ public function jsonSerialize()
         }
         return $this->elements;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Model/Customer.php b/src/Model/Customer.php
index 2593b37..71f810f 100644
--- a/src/Model/Customer.php
+++ b/src/Model/Customer.php
@@ -235,7 +235,8 @@ public function __toString(): string
      * which is a value of any type other than a resource.
      * @since 5.4.0
      */
-    function jsonSerialize()
+    #[\ReturnTypeWillChange]
+    public function jsonSerialize()
     {
         $data = [
             'email_address' => $this->emailAddress,
diff --git a/src/Model/Order.php b/src/Model/Order.php
index e0251f3..893300d 100644
--- a/src/Model/Order.php
+++ b/src/Model/Order.php
@@ -321,6 +321,7 @@ public function addDetailsView(DetailsView $detailsView)
      * which is a value of any type other than a resource.
      * @since 5.4.0
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $data = [
diff --git a/src/Model/Order/DetailsView.php b/src/Model/Order/DetailsView.php
index 496bacf..3026d58 100644
--- a/src/Model/Order/DetailsView.php
+++ b/src/Model/Order/DetailsView.php
@@ -106,6 +106,7 @@ public function setDateFormat(string $dateFormat)
      * which is a value of any type other than a resource.
      * @since 5.4.0
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $data = ['display_as' => $this->displayAs];
@@ -123,4 +124,4 @@ public function jsonSerialize()
 
         return $data;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Model/SearchResult.php b/src/Model/SearchResult.php
index 59b3220..9891d92 100644
--- a/src/Model/SearchResult.php
+++ b/src/Model/SearchResult.php
@@ -39,6 +39,7 @@ public function __construct(Collection $customerCollection, Collection $orderCol
      * which is a value of any type other than a resource.
      * @since 5.4.0
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return [
@@ -46,4 +47,4 @@ public function jsonSerialize()
             'orders' => $this->orderCollection
         ];
     }
-}
\ No newline at end of file
+}