Gift cards are now supported as a special type of discount coupon

When a coupon is marked as a Gift Card, it works as a balance-based payment method: each purchase subtracts the used amount from the remaining balance instead of consuming or invalidating the coupon. Gift Cards can be used multiple times until the balance reaches zero or the card expires. They apply to product and shipping costs (not additional fees). If a Gift Card is expired or has no remaining balance, it will be declined with a Gift Card not available message.