The cerascreen discount codes are usually redeemable only once and only for one specific product. Directly below the coupon code you can read for which product the code is useable. After you have decided which products you want to order you can have them displayed in your shopping cart. After agreeing to conditions of use an sale you can continue to checkout. Here you have the option to enter the discount code in the field provided (see picture).
Afterwards please click on the button Apply.
If the problem is not solved, please contact us by email at support@cerascreen.co.uk.