Fails to Register for Push Notifications

[ghost]

some details here
With a newer version of Play Services, or more specifically, microG GmsCore, the app fails to register for push notifications. The app displays no other information other than that the "Register for Push Notifications" check fails while the other three checks succeed. Other apps, such as Skype and Signal Private Messenger, register just fine.
It has been over six months before the app was updated, perhaps something changed that this app hasn't accounted for yet?

[bbindreiter]

Very likely yes. The production version in Google Play is using an outdated version (9.3) of the play-services library. I'll update everything to the latest and push an update to Play. Thanks for the hint, appreciate it.

[ghost]

I got the update and tried again and it worked; thanks for the fix!