That's very strange, @Nomnomchomp. How about installing the app on a different mobile device? Are you getting the same error when you try to log in?
Please send us a private message with the screenshot of the error message. Thank you.
We'd like to confirm if your TPG account is with TPG ADSL/NBN or FTTB in the event that your TPG account that your trying to log-in is for TPG Mobile service unfortunately its not yet compatible with TPG application.