The credit card in iPhone's iCloud
Settings/Apple ID/Payment & Shipping/Payment Method (Payment Details) has just expired. I received a new card ( new expiration date and verification code) and entered it into Apple Pay a few weeks ago.
Now I've misplaced the new credit card, so I can't update the iCloud payment method for that card. I can enter a different credit card number, of course. But why can't I pay for iCloud with Apple Pay?