With Apple Pay, their payment card has a unique Device Account Number used to process payments and an expiration date associated with that Device Account Number. It won't utilize the actual debit/credit card the account is tied to.
Here's how to find your Apple Card number:
On your iPhone
Open the Wallet app and tap Apple Card.
Tap the card number icon
, then authenticate with Face ID, Touch ID, or your passcode.
Next to Card Number, you can see your Apple Card number.
On your iPad
Open the Settings App.
Scroll down and tap Wallet & Apple Pay.
Tap Apple Card, then tap the Info tab.
Tap Card Number, then authenticate with Face ID, Touch ID, or your passcode to see your Apple Card number.
On your Apple Watch
Open the Wallet App and tap Apple Card.
Scroll down and tap Card Number, then enter your passcode.
Next to Card Number, you can see your Apple Card number.
Using Search on your iPhone or iPad
Swipe down from the middle of the Home screen.
Tap the Search field, then enter "Apple Card number".
Authenticate with Face ID, Touch ID, or your passcode.
Next to Card Number, you can see your Apple Card number.