Why i can’t add my card to my account

There are several things to check when a card cannot be added. Here are suggestions on what to do to try to resolve the problem:

Check that you're able to use Apple Pay:

• • Contact your card issuer to see if they support Apple Pay.
  • Update to the latest version of iOS or iPadOS, watchOS, or macOS.
  • Make sure that you are in a supported country or region.
  • Check that your device is compatible with Apple Pay.

Check for services outages or connection issues.

If you see the message "Could Not Add Card" or "Invalid Card," contact your bank or card issuer.

Apple does not approve or decline cards for use with Apple Pay. If your card was declined, contact your bank or card issuer.

Note: this was copied from here:

If you can't add a card to Apple Wallet to use with Apple Pay - Apple Support