Fixes for the most common sign-up and install problems.
This usually means the link opened inside Messenger's (or another app's) built-in browser, where you're not signed in to Google. Open the link in Chrome instead, signed in with the Google account email you use for the Play Store, and try again. If the group still blocks you, email apps@d11s.space with the Google account email you use for the Play Store and I'll add you directly.
Make sure you've done both steps on the beta page in order (join the group, then Become a tester) with the Google account email you use for the Play Store. If your phone has more than one Google account, the Play Store must be using that same one. Install from the link on the testing page rather than searching the Play Store.
The beta is Android only for now. Let me know you're interested, and if enough people ask I'll build the iOS version sooner.