I too had this same problem. You might try downloading a different web browser or updating your existing browser. I was on a Mac using Firefox, which wouldn't let me sign in (I got the "unable to verify your account" message), so I decided to go to hbomax.com using Safari, the Mac's web browser. This actually worked. Not only that, but I'm now able to simply hit hbomax.com within Firefox, and now I'm logged in while using Firefox.
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