The first six numbers of a card are the IIN or BIN (Issuer Identification Number and Bank Identification Number, respectively). These numbers are not required for a refund and are never provided for safety and security reasons.
Federal Law requires all businesses to truncate credit card information. You only need to provide the last 4 digits for a refund.
One of the security features of Apple Pay is that your account information is not shared with anyone and this includes the merchant, Apple, your device and you. When you enter your card information on a device the number is encrypted and unencrypted information is deleted. Only your bank has the key to decrypt the information and they’re not sharing with anyone.
Ask to speak to the store manager. This can’t be the first time they’ve had to refund an Apple Pay or Tap-To-Pay transaction.