A gift card's value and its price are set separately, so you can sell a gift card for less than it's worth. For example, a customer pays $950 for a gift card worth $1,000.
Steps
Go to Settings > Products > Gift Cards and open the gift card.
Check Amount is the value of the gift card, for example 1000.
Under Pricing, set Full Price to what the customer pays, for example 950.
Select Save.
What happens next
Customers pay the Full Price, and the gift card can be spent up to its Amount.