Apple Cash card is a prepaid debit card and as such, does not have an expiration date. If a PIN is needed for the refund, use 0000 (4 zeros).
Get a refund for purchases made with credit or debit cards using Apple Pay - Apple Support
Get a refund to a payment card that you use with Apple Pay
- If the merchant needs your payment card to process the refund, open the Wallet app on the device that you used to make the purchase.
- Tap the card that you want to be refunded.
- Double-click the side button. You might need to authenticate with Face ID, Touch ID, or your passcode.
- Hold your device near the contactless reader.
Your refund might take several days to appear on your card statement. <<
The merchant should be able to do a >card not present< refund.