After placing your order you have 30 minutes to cancel the transaction. You can then reorder using a coupon code. To do so, please click Have a coupon code located below the shipping options in your shopping cart. To view how much time is left to cancel, view your order details on your Account settings page.
If you are past 30 minutes and the coupon is still valid, you may contact support using chat or email to retroactively apply. This excludes any volume related discount codes.