Redeem Google Checkout coupon on Google Play Are Google Checkout coupons redeemable on Google Play?

I've created a coupon on Google Checkout for a paid Android App on Google Play but when trying to buy it as a user, I can't find the place to enter it. On one device I saw a "Redeem" option along with the credit card but when I entered my coupon code, it returned an error message. Is there any way to make this work?
There is no way to use coupon codes with Google Play.