In order to use gift cards, first, you need to create a new "part" category only for gift cards.
- Go to "Inventory management" / "Product/Job code management"
- Click on the spyglass next to Category,
- Click on the "+" sign and create a new category.
- When you create it check "Inventory follow up" box and "Block list price inferior to the cost" box
- Leave unchecked "Allow product purchases" because you won't need to purchase the items in this category.
As soon as your Gift Card category is created you can start creating products associated with it.
- Go to "Inventory management" / "Product/Job code management" and click on the "+" sign to create a new product
- When you sell a gift card to somebody the quantity filed should be positive
- When you apply a gift card to the customer's invoice the quantity field should be negative.