My reading of Cybersource doc is that if you want to customize the default error (or "reason code") message that a customer sees when a transaction fails (and the default messages always 100% suck) you need to do it on the web server that's serving the message. In the case of a Foxycart hosted cart, that'd be Foxycart's web server. What options does Foxycart provide for me to customize the message a customer sees if the transaction fails?
PS: <soapbox>I know you guys are growing this baby and feature requests are coming in cuz I read all the threads. But good error handling, unsexy as it may be, is IMHO bedrock to long term success. Small site owners (your initial adopters) tend to think first about features and last about what happens when a transaction goes wrong. They want to assume that every customer is legit, that every transaction succeeds. That kind of thinking doesn't scale, not if solid error handling isn't in place. It may be a bitter pill to swallow for the guy trying to sell some beautifully original t-shirts, but the reality is that the first time a customer get at an error message that comes straight from a payment gateway that customer is likely lost forever. You've blown your first and best shot at what could have been one of your best customers.</soapbox>