Finally got access to the site when it was up, found a time that worked for me, tried to buy a ticket. The form required not just the usual name/address/email/credit card number, but date and place of birth, gender, and a few more questions that had nothing to do with a simple financial transaction. At that point, I opted out of that site.

I was able to book a ticket for the Galleria Doria Pamphilij with only the usual name/address/email/CC, so opted for that.