To redeem a coupon or promotional code at MLB Shop, a customer should first visit the official MLB Shop website and browse for the desired items. Once they have added the chosen products to their shopping cart, they can proceed to the checkout page. At this point, there should be a designated area labeled for coupon or promo code entry. The customer should type or paste the coupon or promo code in that area. It is important to ensure that the code is entered correctly, as any mistakes may prevent the coupon from being applied successfully. After entering the code, the customer should click the relevant button to apply the discount. The total amount should then reflect the adjustment according to the coupon or promo code used. Should there be any issues or concerns during the process, customers can refer to the help section on the website for further assistance.