Please also check that the products you're trying to purchase are coupon eligible. Certain vendors don't accept coupons, and certain types of products (like software) also don't take coupons. There should be an icon next to the price that looks like a ticket. Red means not eligible for coupons, green means eligible. You can also hover over the icon, and it'll say.

If this doesn't help, please submit a support ticket (like RedPhantom suggested).

Thank you for shopping with us,

Laura