HBO Max "Can't Verify Your Subscription"

I have AT&T Fiber Internet 1000, and I began subscribing in November 2021. I tried to activate my HBO Max account last week when I got a flier in the mail reminding me that access is included in my internet subscription, and it specifically mentions that I hadn't yet activated the account. I have tried to log into HBO Max using the same account information as my internet log-in on both my TV and on my desktop, but on both occasions, I get the following error message from HBO: "Can't Verify Your Subscription. It looks like your account doesn't have access to HBO Max. If you think this was a mistake, please check with your provider." 

Through my internet searches, it looks like I need to activate my access through my AT&T account before I can use the HBO Max access. However, I've had no luck finding that button/webpage. How do I get access to this feature that's included in my subscription?