Double-check the coupon's expiration date and scope of application. Ensure the coupon complies with the usage rules. Verify with the website's customer service to see if the coupon code is valid. The website may have changed or canceled some promotions. Confirm the source of the coupon; it is possible that the code was obtained from an unrelated website. Ensure the website is fully compatible with the coupon function. If the problem persists, report the issue to the website's support team.