Regarding browser payment API, I had this in mind : https://developers.google.com/web/fundamentals/payments/

Credit card autofill never really worked for me (either on chrome or firefox). It happens on rare occasion that my credit card is pre-filled, but most of the time, it's not (not sure why). And you still have to get your phone and copy the 3d secure code from it (although, 3d secure is only used in europe, if I got it correctly). So yeah, credit card is good, but not enough, especially if we want to perform a big amount of microtransactions like the "pay to expand" example I was talking about.