To validate your Apple account you'll first have to follow My Account > Profile > Verification Process and send us, from the card you've linked to your Apple Pay account, the side where the first 6 and the last 4 digits, the name, and the expiry date are visible.
If the above details are not on the same side, you can send 2 screenshots.
If it concerns a virtual or virtual version of the card, you can send a bank statement with details as mentioned above
Example: