diff --git a/src/Response/NotificationResponse.php b/src/Response/NotificationResponse.php
index f1fdec99..b21b281f 100644
--- a/src/Response/NotificationResponse.php
+++ b/src/Response/NotificationResponse.php
@@ -14,7 +14,7 @@ class NotificationResponse
 
     public string $created_at;
 
-    public string $completed_at;
+    public ?string $completed_at;
 
     public string $status;