On the occasions that I am called upon to connect someone’s shopping cart to a payment provider I always have to go to the payment provider, download their API document, read pretty much the whole thing to learn how they pass information around, and then go into implementation.

I think it is high time that all of the “express checkout” providers as well as the “direct connect” merchant gateways get together and publish common standards for their checkout processes just as the w3c does for web pages.

After all, 90% of the calls include the same style of information, and the flow of payments is nearly always the same.

1- Encode cart info into XML or a query string
2- Feed to gateway
3- Get answer, parse for conditions
4- Process on cart

With the new “express checkout” types (Google Checkout and Paypal are all that I have worked on) the flow is similar though more information comes back in the responses.

Were they all using a common protocol this would save Visa / Mastercard / Discover etc merchants a lot of money paying for all of the extra code in their sites to handle the diverse protocols involved.

“But Matt, wouldn’t all of this efficiency cut into your bottom line?” you might ask. It might, but at least my customers would have some funds to spend on other more directly profitable features and enhancements. I’ve never been afraid of “solving my way out of a job” because there’s always a bigger and better problem out there waiting for a solution.