The discount code can be applied on the checkout page.

Step1 - go to the page of the product you want to purchase;

Step2 - click on the ADD TO CART button

Step3 - From the cart page/pop-up click on the PROCEED TO CHECKOUT button

Step4 - On the check-out page there is a field that notes Discount Code

Step5 - Click on Discount Code and enter your promo code

Step6 - Click Apply