Unfortunately I didn't do a good job documenting my whitelist, but I have both *.firebase.googleapis.com and *.firebaseinstallations.googleapis.com in there, which I believe I needed to get Google Voice notifications to work.
Privacy
A place to discuss privacy and freedom in the digital world.
Privacy has become a very important issue in modern society, with companies and governments constantly abusing their power, more and more people are waking up to the importance of digital privacy.
In this community everyone is welcome to post links and discuss topics related to privacy.
Some Rules
- Posting a link to a website containing tracking isn't great, if contents of the website are behind a paywall maybe copy them into the post
- Don't promote proprietary software
- Try to keep things on topic
- If you have a question, please try searching for previous discussions, maybe it has already been answered
- Reposts are fine, but should have at least a couple of weeks in between so that the post can reach a new audience
- Be nice :)
Related communities
much thanks to @gary_host_laptop for the logo design :)

My app required these to work
I just did some tests and found out it's mtalk.google.com for me at least.
I whitelisted this domain and then I was able to receive notifications on my bank app.
Also I allowed Notifications permission on Play Services app. But I can tell for sure the only allowed google domain was mtalk.google.com, I checked the logs.
Can you check if mtalk.google.com is on your block lists?
My case I'm not using a Google app, it's just my bank app, so it might be different? I'll do some more tests later to make sure.
EDIT:
I found this post on /e/OS forum: https://community.e.foundation/t/what-are-mtalk-google-com-and-www-googleapis-com-serving-for/4788/5
According to /e/OS support:
mtalk.google.com is needed by GCM (cloud messaging). For those using adblockers it was always recommended to whitelist it (not block it), otherwise one would have problems with push messaging
I've subscribed to a lot of block lists and aggressively block most stuff by default, and I just confirmed that mtalk.google.com is in my manual whitelist as well. (Could have been for Google Voice or something else)
I found this post on /e/OS forum: https://community.e.foundation/t/what-are-mtalk-google-com-and-www-googleapis-com-serving-for/4788/5
mtalk.google.com is needed by GCM (cloud messaging). For those using adblockers it was always recommended to whitelist it (not block it), otherwise one would have problems with push messaging