I feel like a newbie!

I'm trying to figure out how to pay for the RER B from CDG into the Notre Dame area with our Android phones when we end our trip there on a Sunday. Apparently, people have been having problems having tickets, properly loaded with NFC one with their Île-de-France Mobilités or Bonjour RATP apps, plus others are reporting the onsite CDG machines can become inoperable and guichet windows may be closed.

I need to have personal reports if you can provide them. PLEASE.
Apple experiences accepted; Android experience super valuable.

Backstory: We have been to Paris over and over and over again since 1998. We've used a zillion different methods to pay for the RER/metro as things have evolved over almost three decades, but at the same time, we've tended to use a taxi for our travel INTO Paris the first day. Why? In the old days, the RER B was not luggage friendly and pretty darn pickpocket heavy. Taking a taxi when we were jetlagged to our first hotel was one expenditure we learned to take. But this time, we won't be jetlagged and we won't be carting luggage. We arrive at CDG at the end of our France/Spain trip around noon on a Sunday, and we depart at dawn on a Monday. We plan to zip down on the RER B to Saint Michel-Notre Dame and walk, walk, walk, walk. Or zip around the Metro at will to remember great times gone by.

Recent travel in all other international places has been super easy with our Android smartphones or just use of our credit card taps, and I just assumed that once Paris went paperless for their RER/Metro tix, I would be fine once I downloaded the appropriate apps.

Instead, today's investigation shows constant glitches, more so with Android but often with Apple.

Do tell!

And yes, I do know we could solve the problem by taking a taxi. I think that's how my husband would view his endgame ("keep it simple, stupid"--not that he would use that term as applied to me), but I'm curious as to recent experiences.

Thank you for any personal insight.
AZ