Woo Your Custom Coupon Notices allows you to show a custom notice to the customer when they apply a coupon during cart / checkout process.
Use more informative messages than “Coupon does not exist!” and many other default messages.
You can use placeholders/tokens, which will be substituted with the matching value.
This Lite version allows to customize up to three coupons.
You can test/get the full version at http://www.w34all.de.