Web push notifications support

I am trying to develop web push notifications for my webapp. I am new at this, so I made some research. If I understand well, Web Push Notifications are just in the process of getting standardized.

When Chrome started to support it, it was through GCM, then FCM. You had to register to get a Google Developer project, sender id, etc. (https://developers.google.com/web/updates/2015/03/push-notifications-on-the-open-web)
Moving forward, with Chrome 52 you no longer need to do this, there is VAPID, etc. Web Push Protocol is getting standardized.
(https://developers.google.com/web/updates/2016/07/web-push-interop-wins)

What is the current state of Web Push Support in microg?

Using CM13, latest microG (0.2.4-81), and Chromium, I can not get web push notifications working. GCM works fine for other apps.

I tried with theese examples:
https://gauntface.github.io/simple-push-demo/
https://onesignal.com/webpush

https://fcm-demo-mtbqzgkaoz.now.sh
This site says on the phone:
FirebaseError: Requested entity was not found. (I have seen this at other sites too, so it seems that Chromium is not able to get a Firebase token)

Is the these web push notifications supposed to work with microG?

Thanks in advance!

Begin with the linked simple-push-demo, OneSignal web push page, and FCM demo using Chromium, CM13, and microG 0.2.4-81. Reproduce the FirebaseError and compare the behavior with the linked Web Push, VAPID, and FCM references. Done would require a documented support determination or a clearly scoped implementation path.