Not a valid coupon
If you receive a message "it doesn't appear to be a valid coupon code" while redeeming your voucher, it means you paste it into an incorrect box.
You receive from us a voucher code, NOT a coupon code.
You must paste this code into the “ Voucher/Promotion Code” box.
You can do so when you log in to your GED.com account and click on the “Study” button. Then, please choose “Practice” and click “Buy Subject.” You will be redirected to the product page. When you click “Buy Subject,” you will be redirected to the product page, and you can see the “Have a voucher code? Redeem now” link.
Click on this link and follow the instructions on the page.