After looking at the reviews we picked up our tickets from the referenced bookstore (10 busy street mins away) the day before. On the day we got there early to take some photos and managed to be one of the first few in (Queueing slighty left of the middle out front before the signs etc went up). Inside the Pantheon to the left is where you get your audio guide and headphones, again this was unclear in the description as I was worried you also had to pick it up at the bookstore but no, inside the Pantheon - handed over some ID before following the audio tour around. The audio guide, as well as the incredible Pantheon, was a great start to the days exploring!

It was a good experience, fantastic building and audio guide is good, however the whole concept of having to walk hundreds of meters away from the site, to collect a pre-printed piece of paper with no time slot or ID, to then walk back just to get inside is rather ridiculous. And the time-slot doesn’t mean anything. Just turn up when you want.

The audio tour was good overall. However there is one issue that needs to be fixed by the merchant. We booked our tickets at 11 AM. Whereas once we booked them on the mobile application, the timing showed up as 9 AM. It turned out that we can pick up the tickets at any time and we can visit the Pantheon at any time during the same day. Hope this helps anybody.