If you try to use your Apple Barclaycard VISA via Apple Pay (or any mobile pay, such as Google Pay as I did) in a physical Apple store, don't. The transaction will be immediately declined and your entire account locked for fraud. Calling Barclaycard, I was told by a supervisor that "they've seen an increase of fraud at the Apple Store, so they have specifically blocked NFC purchases at the Apple Store".
So you can use your Apple credit card with Apple Pay in literally any store in the world... except an Apple Store.
So you can use your Apple credit card with Apple Pay in literally any store in the world... except an Apple Store.