For some reason this security setting was turned off on my account even though I don't remember turning it off and use sign in with Google in other places.
Note that if you have added more than one Google account to your phone, this setting must be enabled for ALL accounts (not just the one you intend to use to activate Beeper Mini) or the "null" error will appear.
Was able to fix. I have 6+ Google accounts, and one of the accounts didn't have it checked, so it needs to be all, instead of just the account you're looking to connect.
https://help.beeper.com/en_US/beeper-mini/beeper-mini-how-to...