Here's how to use Promo Code when shopping in StockX: add new products to the StockX shopping cart and click the checkout. Log in or create a new account to StockX by entering details, then click Continue to pay. Below the listed items, you will see a box that says Add Coupon, choose the StockX Promo Code you are going to use and then the website will automatically return to the checkout page. Now you will see your actual total payment at stockx.com.