Check the fine print for any exclusions or restrictions on the coupon code. Ensure the code hasn't expired and that it meets the minimum purchase requirements. Verify the spelling of the code and try entering it again. Clear browser cookies and cache or try using a different browser. Disable browser extensions temporarily, as they might interfere with the code. Contact customer service for assistance if the code still doesn't work. Search for a new working promo code if the current one is invalid.
