Apologies, I generalized on the in-app browser front... On Android it is shared so I assumed it would be the same for iOS. I think that if you do not want to use it on your browser the only solution would be the gmail login in the home screen app. I replied to that specific part via email since it involves your email address. Thanks and apologies for the inconveniences.
Viewing post in Play the augur on Phones and Tablet comments
Thanks! This is resolved.
For anyone who runs into this in future, Google login worked fine with an @gmail.com account. The error seems to somehow have happened because I was using a Google account created as part of “Google Apps for Your Domain”. Google’s error was entirely misleading on this front, so, go figure.
TL;DR: Don’t use an organization/business Google account, just a regular Google one.