How do I return an item purchased with Apple Pay in stores?
You take the item(s) back to the retailer as normal. Some retailers will be able to offer refunds back to the device from which the original payment was made, while other may have to refund the plastic card.
If the retailer is able to refund the device used to make the original purchase, you:
You may need to provide the last four digits of your Device Account Number to the retailer. This can be found by opening the Wallet app on your iPhone, tap the card and tap the () symbol and then scroll down to find Device Account Number.