Hi,
From the error, it seems sender agreement missing for response. Make sure you have created synchronous interfaces for both inbound and outbound structure and 2 mappings (one for request and other for response) are to be assigned to the Operation Mapping request and response tab respectively.
You need to create both sender and receiver HTTP_AAE channel and need to call the modules in the sender channel and put the parameters as the receiver channel. You need not mention receiver channel in ICo, the sender channel will call receiver channel through module(exactly like you call a function inside another function.).
Try and let us know.
Suman