Answer
Most retailers place the promo-code field in the basket, order summary or payment stage. Look for labels such as promo code, voucher, discount code or offer code, then apply the code before paying.
If you cannot see a code box, the retailer may apply the promotion automatically, hide the field until a later checkout step or restrict codes on that sales channel. Do not complete payment until you have checked the final order total.
What to check before checkout
Read the retailer’s current promotion terms, confirm that the code applies to the items in your basket, and make sure the expected saving appears before you pay.