Circumvesuviana tickets

Circumvesuviana tickets are cash only and in person at a ticket window.
Here is the schedule:
https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule

There are easy-to-use ticket machines on the level below the main train station in Naples. There's signage, but it took me a few extra minutes to find the right place. You board the train near the point where you buy the tickets. The impending departures are listed on a monitor. Look for a train with a destination of Sorrento.

I think those machines only take coins also.

I think I'd remember having to feed in coins, but maybe not.

I read somewhere that you can buy a ticket by tapping your credit card as you board the train. Can anyone verify this from personal experience?

I'm sorry; I didn't notice one way or the other. I wouldn't risk trying that unless a very reliable source confirms it. It's easy to buy the ticket before getting on the train, and you wouldn't want to risk a fine; I believe it's at least 50 euros even when the ticket you do not have is super-cheap.

We rode it multiple times last week, to a from Naples, Herculaneum, Pompeii and Sorrento and a couple other lesser known stations.

• You can't buy online, but there are ticket booths at each train station. It's a regional commuter train so no worry about not getting a seat.
• I never noticed a ticket machine, but there could have been.
• The ticket booths take credit cards, in fact a couple of times when I tried to pay cash, I was rejected because they said they didn't have enough change.
• There are no machines on board to tap and pay, you need a ticket to feed into the turnstile to get on the platform.
• I don't know what the fine is for travelling without a ticket, but in the many times we rode it, we never saw security or ticket checkers, ever.