How to Get Coupons Working in Zen Cart with Google Checkout Plugin

I installed Zen Cart store for client (version 1.3.9h) and we added Google Checkout addon (version 1.4 +0.9). The module claims to be from version 1.4 "Support for ZC coupons even using a flat rate". However, entering a coupon code into Google Checkout results in an invalid coupon code error.

We have enabled and created coupons in the system.

Any help in understanding what's going on here would be extended. The store is still in beta for EncoreDT.com .