You can enter any promotional codes you have in the basket. Enter the relevant number and click redeem. The total should then update. If the code doesn’t work please check that it is in date and you have the added the correct products to your basket to qualify for the discount.
If you have found a code on a ’money saving’ website, don’t be surprised if it doesn’t work, as most of these will have expired or will only be usable by certain people.
This most likely means that the item is sold out. If it’s a popular release the product usually sells out quicker than it can be removed from the website. Alternatively, it could be an issue with the payment process, in which case, give our customer service team a ring and they will assist.