Gift Cards need to be attached to an account. When you click the "Redeem" button in the email, follow the prompt to either log on or create an account.
Once your Gift Card is credited to your account properly, it will show up on the left hand side of your profile.
If it is not working when you checkout, please make sure you enter the amount under "Gift Card Balance" in numbers only. Do not include a $ sign. If this does not work, please contact us at firstname.lastname@example.org.