Unable to request body in rest connector

Let me explain the overall flow i am trying to achieve. The flow is exposed as rest service to client. Client will call the rest service to send a file to a specific location. Client will trigger the flow, there is a requirement where i need to call a rest service inside the flow . Client is passing the required data in headers and the same header values i need to set while calling the rest service. I tried adding rest connector but body is disabled. I am not able to send custom request body to a service through rest connector. can you please guide me how to do it.