Do not pick a payment method for “the China metro” in the abstract. Find your city and operator first. Shanghai's official visitor guidance gives several workable choices, but those choices do not establish acceptance in another city.
Start with the operator's current options
Check the metro operator or city transport portal for the line and station you will use. Look separately for gate contactless payment, a ticket sold at a station service centre, a local transport card, and an app QR code. A card that works at a staffed desk may not work directly at a gate. An app may need identity verification or a linked payment method before the first ride. If the page is old or silent on your station, ask station staff before entering.
What Shanghai officially lists
The Shanghai municipal visitor guide describes contactless card payment at equipped gates, QR travel through Suishenxing and the Shanghai Metro Daduhui app, and a single-journey ticket bought with staff help if the passenger lacks a bank card or payment app. It lists selected international card brands for the app, but card acceptance still depends on the card, issuer and payment setup. A separate Shanghai municipal notice on station service centres says foreign cards can be used at service-centre POS machines to purchase metro tickets. This is a counter purchase, not proof that every foreign card can be tapped at every gate.
Choose a fallback before the first ride
If you want to use a card at the gate, check that the station and gate display the supported contactless symbol and confirm with staff if uncertain. If an app code fails, go to the station service centre rather than trying repeated payments without knowing whether a fare has been charged. Ask for a single-journey ticket and which payment methods the desk accepts. Keep the ticket or app record until you have exited. If a bank card is declined, ask the issuer whether transport transactions are enabled; the metro staff cannot make the issuer approve it.
For another city, repeat the same check against that city's operator. Shanghai's app names, card acceptance and station equipment should never be presented as a nationwide rule.