Some AT&T customers who are supposed to be able to get HBO Max as part of their plans have been having trouble accessing the service via their AT&T accounts. There have been a number of complaints about this issue on social media platforms. The good news is that while it might have been annoying you all day it is easily fixable.
The fastest and easiest way to get this situation resolved, and most of the time anything else with AT&T is via chat.
If you are having problems getting HBO Max Autherized through AT&T go here and scroll to the bottom of the page where you will see an option to chat with a person. Tell them your issue and just be ready with your member number etc.