First of all, the information you seek is contained in the following header file:
httperr.h
However, as is usually the case, you have to dig through this file a little to find what a return code of -7360 actually represents.
First of all, you'll notice that there is a constant defined around line #145 called KHttpErrorBase with a value of -7200.
Then, around line #496 is another constant called KErrHttpMissingHeaderBase with a value of KHttpErrorBase-160.
Finally, around line #503 is the constant your actually looking for called KErrHttpEntityHeaderMissingContentType with a value of KErrHttpMissingHeaderBase,
So, at the end of the day, -7360 translates to a missing Content-type header in your request.