I'm far from a tech person, but there are always things you can try.
First, is this a membership site? If it is, the cookie (saved bits of computer code that signs you in) might be corrupted. You can delete your cookies, or just that one, and try again.
Have you tried accessing it on another internet browser (Firefox, Safari, Chrome, Edge, etc.)? Lots of times what Firefox won't accept, Chrome will allow, for me anyway.
Do you live in a state or place that restricts access to adult materials? Then you'll want to get yourself a VPN to disguise your location.
If none of these things makes a difference, those who are far more tech than I will want to know what kind of device you're on, what software it's running, what browser(s) you use, i.e., I'm on a laptop running Windows 11, and I was using Firefox.