7 Eleven Payment API

Hi,
I’m trying to find a ready built API or plugin that would allow 7 Eleven Counter Services to send a Request to my Woocommerce MysQLDatabase when a user goes to pay for goods ordered online. The API needs to get the amount payable, name, product etc, return that to the store, accept payment and then update the database to paid status. 7 Eleven want the data exchange in XML with a number of custom parameters not found in woocommerce’s tables. I have very limited knowledge about this kind of API and am willing to spend the time and effort tom learn the required skills to build it myself if there is no other way. But the market is flooded with applications, languages, formats etc, and I need advice where to start.