Just present it when you oay the check. If the bill is more than the gift card, they'll ask for additional $. If the bill is less than the gift card, you'll have a balance and can use it again next time
Use it same as credit card if there is a difference in the bill you have to pay the additional cost or if it's less they will leave it on your gift card or you can leave it as a tip be the same as cash for the waitress waiter
Just present your gift card they will adjust the balance whether it's higher or lower
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