[ahopebailie]

Google have some great ones which are applicable across the board (it's a standard!), but they are busy being updated: https://developers.google.com/web/ilt/pwa/introduction-to-th...

also: https://developers.google.com/web/fundamentals/payments

There is also some good content on MDN: https://developer.mozilla.org/en-US/docs/Web/API/Payment_Req...