I Hope this can help someone. I had the same issue as everyone. I had HBO Go with my unlimited plan, and when they moved to HBO Max I could never get passed the login screen and kept getting subscription not verified. 
I saw someone here post a recommendation and it worked. I was using my old username that I used with HBO, at some point ATT changed it to emails but allowed users to keep their ID which kinda split your account to have 2 different IDs. I recommend you go to your ATT profile and update your login to the same email address used by your account, you can also use your phone number. Once I did that I was able to login to HBO Max with no issues. 
I hope this helps. 

Hey everyone if your using a phone go to internet browser settings and change yo desktop view and you'll find the option to activate on account overview. If you can't figure this out just use a laptop. Phone view doesnt show the full page in which the activation button is on lol

Hey everyone if your using a cellphone make sure to go to your browser setting and hit on desktop view then go to your account overview to hit activate HBO max. When using phone view the page doesnt show the whole page including the activate button. If you cant figure this out just use a laptop or desktop and go to account overview and you'll find the button to activate. AT&T customer service is either uninformed or literal knows nothing of how the page is designed. 

This doesn't work. Can we take legal action? Wondering what next steps here are to get HBOMAX as we're paying for it!

If there is a (Edited per community guidelines) reading this, please contact me and I'll be happy to help you take legal action against AT&T for scamming its customers. I have Unlimited Elite, but after HOURS of phone "help" nobody solves the issue or calls me back. I am paying for HBO Max, but they don't provide it.

Scroll down to this post. It has the answer. You must create an account on ATT TV and activate HboMax through there first and then sign in with that account. 

I finally found someone at ATT who was able to figure this out. Supposedly, the issue for my account happened because we have been ATT clients for a long time and were grandfathered into the plan that includes HBO Max. Because of that, the "normal" pathway to get this benefit doesn't work, even though we were signed up for a plan that included HBO Max.

This is what I did while I was on the phone with someone from ATT who was looking at my account. I am not sure what had to happen on their end, but this was the process from my end.

I signed into my ATT account on my computer.

I then sent a text with the word "LICENSES" in all CAPS to the number 2885

Then I sent a text with the word "MODIFY" in all CAPS to the number 2885

Then they had me make and account and sign into the website www.atttvnow.com USING THE SAME USER ID AND PASSWORD as my ATT account.

I had to select HBO Max only (not the option to purchase a plan with all HBO features).

Then it opened the HBO Max feature thru the https://www.att.tv/

website.

At first the ATT person thought I would have to access HBO Max thru the https://www.att.tv/

website in the future, but then she saw that it had converted my account to HBO use, so we now can log in thru the HBO Max and website directly. Once this worked on my computer, she had me test an additional ipad (or iphone). It works now.  Good luck. It took me 2 hours and a few people from HBO and ATT to find someone who could fix the problem.

I FINALLY FIGURED IT OUT.  I have the unlimited elite plan.  I got a new iPad and couldn’t figure out how to login to HBOMAX app.  The problem was that the HBOMAX app only displays AT&TTV as a provider!!  Scroll to the bottom of the provider list and select “OTHER”.  There you will find “AT&T” which worked  immediately with my AT&T login credentials.  Hope this helped someone.

We have enough people on here to start a (Edited per community guidelines) (Edited per community guidelines). I have had Unlimited Elite for the several months, and suddenly HBO Max stopped working. I don't even have HBO Max section on my AT&T section on my account page now. HBO Max customer support is telling me to go to AT&T and AT&T is telling to contact HBOMax. My HBOMax account section tells me that my subscription through AT&T has expired. My AT&T account doesn't even show HBOMax access. And I have AT&T Unlimited Elite! It has HBO Max! I was on hold with AT&T for over 2 hours the other day, nobody ever picked up. I tried to call them several times but never been able to reach them once. Short of suing them, I don't know what can help.

Need Help!  I have Unlimited Elite, a qualifying plan, but my AT&T account page has no information on how to activate HBO Max, as your website says it should!

Please help!