Double-check the coupon's expiration date, scope of application, and other restrictions to ensure it complies with the usage rules. Verify the coupon code with the website's customer service to see if it is still valid. Ensure the items in the cart are eligible for the discount. Clear browser cookies and cache, then try applying the code again. Use a different browser or device to see if the issue persists. Check for typos in the coupon code. If none of these steps work, the coupon code might be invalid or expired.
