pushnotification

I would like to use Pushnotifications on my forum. The system requires gmp which I think is turned on in DirectAdmin, by CustomBuild 2.0. At the moment the management pagina in XenForo tells me there is no gmp and phpinfo.php also won't show any gmp. I switched gmp on in CustomBuild and...

Error: Call to a member function getStatusCode() on null src/XF/Service/PushNotification.php:211 Stack trace #0 src/XF/Service/PushNotification.php(168): XF\Service\PushNotification->handleResults() #1 src/XF/Service/PusherTrait.php(182): XF\Service\PushNotification->sendNotifications() #2...