diff --git a/src/BusProNet/ApiClient.php b/src/BusProNet/ApiClient.php
index fd1db9b..8f65b5a 100644
--- a/src/BusProNet/ApiClient.php
+++ b/src/BusProNet/ApiClient.php
@@ -83,7 +83,7 @@ class ApiClient
     /**
      * @throws ApiClientException
      */
-    public function register(RegistrationData $registrationData): Notification
+    public function register(RegistrationData $registrationData): ContactFormResponse|Notification
     {
         $data = [
             'user' => $this->config['bpn_username'],