If there is a discount code associated with your account, a section should appear in the "cart summary" during the checkout process to enter this code and apply it to your order.
It should be displayed as follows:
To apply the discount to your order, all you have to do is enter the code you have received in the corresponding field, and then click on the "Apply code" button.
It is important that this is done before finishing the purchase process, as once the purchase process has been completed and the invoice has been generated, we will not be able to apply the discount.