UnifiedPush with Sunup

Actual behaviour

UnifiedPush with Sunup (https://f-droid.org/en/packages/org.unifiedpush.distributor.sunup/) is not working. The UP endpoint can be registered by FMD Android, but a push is never received.

Expected behaviour

It should probably be working? Try to investigate if it is failing on FMD Server side, Mozilla's side, Sunup's side, or FMD Android's side.