A recent change to HBO GO means you must create a new HBO GO ID.
It's an easy, one-time process.
The next time you sign into the HBO GO app with your Frontier ID, you'll be asked to create a new HBO GO ID.
If you want to re-use your previous HBO GO ID, click the link at the bottom of the form to contact HBO. HBO will delete your old HBO GO ID so you can re-enter it for this new registration process.
Circled below is the registration screen you'll see. Simply fill in the form and get back to watching HBO.