Train ticket purchase between Sorrento to Pompeii

This commuter train is very cheap, and there's no reserved seats. You can buy round trip tickets at the station the morning of. From our experience, around 9:00am, the morning train isn't crowded out of Sorrento.
However, the return train from Pompeii to Sorrento was packed, SRO, no air conditioning, mid-May, midafternoon. The train ran late and the trip back took twice as long as the morning train. For the tunnels, there's a single track, and as the trains run late, they have to wait for their "turn" through the tunnels. This happened multiple times. I can't describe the misery, standing in a very hot train car, after being on our feet all day at Pompeii. Be prepared mentally.
PS
My husband also caught covid during the experience, and brought it back home, then I got it. So I will never forget that trip, two years ago. ( I masked, he didn't, standing shoulder to shoulder.)
Wishing you a wonderful trip. Safe travels.

No
You must buy at the station
You can buy day of, day before or whenever you like
Tickets are not train specific, no assigned seats
It’s basically a commuter train

Be sure to validate
Buy your return ticket in Sorrento as well

It will probably be busy
Train starts in Sorrento so you should be fine but I would get there early and line up if you want to be sure of a seat
Return train will be very crowded probably no seats

Circumvesuviana is a private line or train. Not part of the national rail system so you buy your tickets as a walk up. Single price as it is basically a commuter train. Just buy at the ticket window. It is part of the Italian experience.

I am going to take the Campania Express from Pompeii to Sorrento. I saw when I typed in Campania Express I can purchase tickets online. It directs me to the website "Sorrento insider". This site then takes me to the Campania Express site. To book the train ticket It then says "book.distribution.com. Are these legitimate sites? They look legitimate.

Hi - how do you validate the ticket for a regional train? I purchased Trenitalia tickets from Montecatini to Verona and the second half is Frecciarossa so I have a seat assignment and a QR code for the conductor. But the first leg of the journey is from Montecatini to Firenze and the ticket is for a Regional train 2nd class and I printed something that has a ticket code but there is no QR code. At Montecatini Centro do I punch in my ticket code to get it validated? Just not sure of the process. Thank you very much

OP post is about the Campania Express
Your question should have its own post/subject

If you have a paper ticket validate in the machine at station

If digital you validate on the app

You might find this useful
https://www.seat61.com/train-travel-in-italy.htm