What's the best way to buy Colosseum underground night tour tickets?

A few years ago I went to Italy, i had tickets for the Colosseum underground night tour, but my reservation and name were lost "in translation", my name wasn't on the paper so I couldn't get in. I'm going back to Rome the 21st and 22nd of May, and this time I really want to visit the Colosseum.

So first question, is the underground night tour of the Colosseum the "best" one if you're a movie fan like me and want to see gladiatorial history and all of that?

But the most important and second question, what's the best way to buy those tickets, I'm trying on the official website, but when I click Buy Ticket, it's always 404 page down.

https://colosseo.it/en/tickets/a-night-at-the-colosseum/Colosseum