One of the most frustrating coupon experiences happens when the same product worked with a coupon last week, but the register rejects it today. The product may look identical, and the coupon may even appear to be the same one you used before. However, coupon terms can change based on the promotion period, purchase requirements, or retailer rules. A coupon that was valid last week may have expired, reached its redemption limit, or become unavailable for a particular purchase. Before assuming the store made a mistake, check the coupon details again and compare them with your current transaction.