When adding exchange items to a return using the returnCreate mutation, we are using the giftCardCodes field (on the ExchangeLineItemInput) to apply a gift card to the exchange items. The gift cards we are applying are active, have no expiration dates or conditions, but nothing happens when we use the giftCardCodes field. We get a successful response and the return is correctly created with the exchange items, but the gift card is never applied. Am I misunderstanding how that field works or is this a bug in the API?