Cordova-plugin-firebasex no background push notifications on iOS

Sending push notifications to the app only works in the foreground.
There is possibly a problem with the apns. I uploaded the AuthKey (.p8) from the apple developer account to firebase.

I tried the cordova-plugin-firebasex-test repository where I receive the message in foreground as well. If I click on getAPNsToken() it only returns null

Code:

if (this.platform.is('ios')) {
      this.firebase.grantPermission().then(() => {
        console.log('permission granted!');
        return;
      });

      this.firebase
        .onApnsTokenReceived()
        .subscribe(token => console.log('APN-TOKEN: ', token));
}

this.firebase
      .onTokenRefresh()
      .subscribe(token => console.log('TOKEN: ', token));

this.firebase
      .onMessageReceived()
      .subscribe(data => console.log(`FCM message: ${JSON.stringify(data)}`));

onApnsTokenReceived never get called.

What did I wrong or haven't configured?