mine apple pay app is not working. please help

Apple Pay is the way to pay. It replaces your physical cards and cash with a method of payment that is private, easier and safer. Whether you pay in a store, on a website or in an app. This is the new payment.

See -> Use Apple Pay for contactless payments on iPhone

Use Apple Pay for contactless payments on iPhone – Apple Support (UK)

See if anything here helps.

Apple Pay - If a payment card that you use doesn't work.  *