External Rest Service Exception

I am trying to set a call to an external Rest service.

I have set up and tested with Postman and it works.

But testing via the Connector service request I get the following

{

  "Exception": "com.oracle.e1.aisclient.JDERestServiceException: com.oracle.e1.aisclient.JDERestServiceException: JDE Rest Service Call Failed: Status: 400 {\"statusCode\":400,\"error\":\"ExternalRestService:callGeneric: External Call Failed External Generic Call Failed See Log For Details: 400 {\\\"error\\\" : {\\\"code\\\" : \\\"REQUEST_PARAM_REQD\\\", \\\"message\\\" : \\\"This request is missing a required parameter.\\\"}}\"}\n"

}

I have set up a connector with an end point ,  no Security

In  my service request HTTP method is POST