On the order form, after you enter your promotional code into the "Promotional Code" window in the "Review & Place Order" screen, be sure to click the "Apply" button to the immediate right of the box where you entered your coupon code. A "Disc. Price" column will then appear with the discounted price of the item(s) in your order. After that, click the "Place your order" button, and your order will be submitted with the discounted prices.
Promotional codes cannot be applied to an order that has already been placed, so please be sure to apply your promotional code to your order before clicking the "Place your order" button.