For reference, he's talking about the code that appears in the screen shot below. From my own digging into this I understand that Marketo uses typical HTTP response codes here, but they also have custom responses. The only example I've been able to find in the
Marketo community is that a response code of 1000 means "cannot call webhook in batch campaign". I've personally encountered a 1001 response code, but I can't find any documentation that explains what it means. Like Greg, I'd also like a list of response codes and detailed descriptions of what they mean.