I want you to understand how this std. iflow works.
ECC webservice is used as Outbound webservice in C4C. So, by the time the call goes out of C4C, structure of the call will be of ECC's but not C4C's. Got it? So, both sender and receiver of this iflow are actually ECC's. 
So, you have to use the same schema in both Source and Target of mapping. Mappings in iflow are not a scenario specific development. They are supposed to be done that way.
Next thing, tracing your calls in ECC. Go to srt_util and add your service user over there and trace the payload. This transaction is to be used only for webservice calls. Good luck.