Hello, XfinUser2019. Welcome to the Xfinity Forums!
I appreciate that you reached out to us with this concern and I would love to help.
Are you able to access HBO content using the Xfinity Stream app?
If not, you may want to review your service bill and make sure you are subscribed to HBO content. If you are able to access HBO content using the stream app, you can try uninstalling the HBO Go app and re-installing it. Alternatively, you can try signing in with a secondary username to see if that one works.
Please let us know if any of that helps or if you need further assistance.
XfinUser2019, as I have not heard back from you in some time, I have closed this thread to further comments. I hope you were able to regain access to the HBO app, but if you still need assistance, please feel free to start a new thread.