At first, we would like you to confirm whether an error exists.
Please go to the last check-out stage, where you can add the discount code once again. The first 'stage', a.k.a. shopping cart, where you have your items in the basket does not subtract the costs, but if you go further to the second 'stage' where you need to enter all the shipping information, it asks again to apply the discount code, hence it should work.
If it still does not work, please get back to us at firstname.lastname@example.org, and we will be more than happy to help you out!
Remember only one discount code can be applied!