Contact your respective financial institution for questions or issues related to: declined payments, making credit card payments, disputing charges or payments, canceling a card, reporting a card lost or stolen and requesting or replacing an ATM/Debit card.
With iPhone X
With Other iPhones / iPad
Supported Apps has an option to 'Buy with Apple Pay' at checkout and may allow you to enter card info, shipping, billing and contact info.
The way the apps present the option may differ, but always has the Apple Pay logo.