You can get the free transfer with a card, just not with applepay, googlepay, etc. (I think this is because those systems randomize the card number. Obviously, if you want the free transfer, you have to use the same credit or debit card.) The app to engage OMNY ( the subway's system) directly is forthcoming supposedly in 2021, as is the ability to use unlimited cards through the app. Right now many of us still have to use a metrocard as a result.