Anthony from the App Distribution team here. We have found the root cause and pushed out a fix yesterday.

It turned out that we were not handling the iw locale properly (which is an old, deprecated version of he that some devices still send). Now, we properly load the page and show Hebrew for that specific ISO 639-1 code.

Testers should now be able to use the site without issue. Sorry for the inconvenience!

I had the same issue, I finally managed to narrow down the issue to the browser type which is launched once clicking on the invite link. On Samsung devices, the default browser is "samsung interent" which couldn't handle properly(not sure why) the invite link, once setting the default browser to chrome everything worked as expected.

I've just managed to solve this issue on Galaxy Note 10.. had no problem on Galaxy S9.

Solution: 1 - Following the answer from Evgeni Roitburg I've copied the actual link from the "accept" button, using the "share" function and sending it to myself.. and opened it manually in Google Chrome, but it still gave me "404"..

2 - Out of instinct I've tried to change the phone language to English, it was in Hebrew.. After that the link started to work when opened in Chrome.

Need to mention that I've also made sure that the "user" on this phone's GooglePlay is the same gmail user which was invited via Firebase.

It seems that there is no mentions of this issue in the internet after searching Google a little.. Hope this solution will help you.