This is what I did that worked for me. I logged into HBO GO website through the Chrome browser on my phone. It takes you through the same steps as in the app, except when i selected Xfinity as my provider it didn't give me the error and i logged in just fine. Then after this i left my browser open and switched to the HBO GO app. This time when I selected Xfinity as the provider it didn't give me an error. I hope this helps since 3 phone calls to Xfinity help and Advanced Tech support did nothing.
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