For 2 of our day trips in Rome, we are using transportation that is run by Cotral. (Once going to Ostia Antica ( Roma-Lida line is now called Metromare and is run by Cotral, not ATAC anymore), and also going to Tivoli on a Cotral bus.)
I will be using a credit card with the "tap and go" feature instead of purchasing a paper ticket. If asked for proof of purchase of my ticket once on board these transports, I believe I just show the conductor or "ticket checker" -- if there is one-- the credit card I used with the tap and go machine--is this correct?
I have read in depth all about tap and go ( including ATAC website info), when they talk about using "tap and go" on Cotral run trains and buses, the language is a bit confusing. They talk about needing to download an app to show proof that you've bought your paperless ticket --BUT only for Android users. I have an iPhone, and do not use the "smart" feature to pay for things--only a credit card.
Sorry to be dense about this. I don't want to be fined...:)