I've noticed that discount codes are not being sent in the XMl from the API. Our client is implementing some new accounting software and needs those codes for reporting.
We are on store version 0.7.0. Doing some digging and it looks like those stopped coming when we upgraded our store version. That's a guess on my end but it all happened around that same time.
Here is a sample of the discounts XML returned by the API for a recent transaction that used a coupon. As you can see...the code parameter is empty when it should show the coupon code: