I have to admit, as many years as I've used FoxyCart, I've never interfaced much with the datafeed (if at all). I'm getting a little tripped up.
The only use or function I have for the datafeed at this time is to have my PHP script (after successful ordering and payment) log our database with some data indicating that a special "code" has been used/redeemed, and cannot be used again. From that standpoint, it's a simple MySQL update query, but I'm not sure I'm using the datafeed right.
Other than the query I need to run in my PHP script (the datafeed URL), do I need to do anything else other than to echo "foxy" out to the page? Maybe that's all, and I'm over-thinking this.