Pantheon Booking Site?

This is the site for the tickets. http://www.museiitaliani.it You will need to register, but it's quick.

Right now, I am aware of only 1 website for standard-entry ticketing. All you need to know, including link to that site, here:

https://www.wantedinrome.com/news/how-to-visit-the-pantheon-in-rome.html

Be aware that the ticketing link may only work during hours the Pantheon is open but I'm not sure. That's how it works for me for Coopculture's site and a few others. I'm unsure how far in advance they sell tickets. Those may also be purchased onsite if willing to stand in line (go before the opening hour in the morning or maybe an hour or so before closing).

Pantheon's other official website; that one is only booking tours, and an entry ticket - to be ordered from the other website - is also required for those.
https://www.pantheonroma.com/home-eng/

Agree with Kathy that it only seems to be working when the Pantheon is opened. I went on a couple days ago and got registered, but need tickets for September and they were only selling thru the end of July.