This message started appearing 3-4 years ago when you logged in with a prepaid account.

Sorry we’re not ready for you yet. We’re working on improving your app experience. In the meantime, my.t-mobile.com can help you out. Go to my.t-mobile.com

  • paraphrandOP
    link
    English
    19 months ago

    This was updated sometime since this post. Now they are honest and say prepaid is not supported.