Accept the conditions on the first page and on the second page indicate that you are "Non-AT&T Mobility customer" and submit the filled in request.
They are pretty fast these days. If you get a decline resubmit as someone typed a wrong number and in my experience it rarely takes two requests and never more.
I have unlocked 4 devices with them this year using 2 email addresses (limit is 5 per year/consumer) and will soon be unlocking a 5th. Easy peasy. I have never been an ATT customer.