Tips on where to buy metro/bus tickets in Rome for a person who doesn't have their card on their phone?

I have seen here that there are lot of scams with people not being able to validate their tickets. I am travelling with my parent who unfortunately can't pay with their card on their phone but has a physicial card and I have heard of this tap&pay system, is this related to an app or? Where is the easiest way to buy tickets and validate them immediately? thank you for your help in advance!