If your computer has a wide screen, the coupon/gift code box is located in the right column once you get to the Checkout screen.
If your device has a narrow screen, click on " Show order summary" under the KAMsnaps logo.
As a last resort, you can also type the code in the ORDER NOTES box on the Cart page, and the coupon will be manually applied when your order is processed in the form of a refund.