I just recently came back from France where I did the Paris and Heart of France tour, and spent time on my own in Paris. I arrived a couple days before the tour, and had downloaded the RATP app prior to arriving just to get familiar with it. I followed Daisy’s advise and set up a digital card in Apple wallet to purchase tickets. This worked great. When I joined the tour we were all given a physical Navigo card with 10 tickets on it. I had an issue with the physical card, though, as did another tour member. The first time the card worked fine, but when myself and another tour member were returning to the hotel, she got through the fare gate, but I didn’t. At first I thought it was the gate so I tried the next one, and then realized the card wasn’t being refused, it wasn’t registering at all. So, my tour mate stood on one side of the gate while I frantically bought a fare on my digital card to get me through the gate. I gave the card back to our tour guide, and he investigated, and discovered the card had somehow been de-magnetized. Another tour member had the same issue. So, it was fortunate that I also had the digital card set up. At least I didn’t get stuck inside a station and be unable to get out in the case of a station where one has to tap to get out.
Another odd thing happened on the day I arrived. When I went to buy a ticket for the RER B train from the airport, there was some kind of technical glitch and all the machines were down. Staff were standing there just telling everyone to go get on the train, but get off at Gare du Nord and buy a ticket. This made no sense to me as I was going further than that so why should I drag my luggage up to the ticket machines and back down again. So, I had the digital card set up already, and just bought my ticket that way and carried on.
The physical card worked fine for the rest of my Paris stay after the tour, but it might be a good idea to have the digital card, also.