We need an online Shopify store that allows a user to purchase a number of item. However, the item can only be purchased with a gift card from the store and not with a credit card. It looks like we might have to hijack the transaction and ensure either a gift card has been purchased or automate the purchase of the gift card. Also, we need to store the balance of the gift card. For example, if the user purchases an item at $54.65 and we purchase a gift card of $60.00, we need to store the balance of $5.35 for that user.