As gift vouchers are a payment method and not a discount code, they need to be applied to your order once you reach the Payment page.
At the top left of the Payment page, there is a box where you can apply your gift voucher.
After you have applied your gift voucher, you should immediately see a success message and your order total reduced.
You can apply multiple gift vouchers to your order, and they are valid until the full value of your Gift Voucher is redeemed or the Gift Voucher expires, whichever occurs first.
Gift vouchers can also be used to cover the cost of shipping. If there is no remaining balance after applying your gift voucher (and any discount or pre-purchase voucher codes), you will see a message which prompts you to complete your order.
Gift vouchers need to be redeemed by their stated expiry date.