Integration

I have a question about HTTP response codes. Right now I have an Oracle Service Bus proxy for a REST service that does some validation on the query string from the URL. If the validation fails, I want to send back an HTTP status code of 400 BAD REQUEST but cannot figure out how to do this. Does anyone know how to change the status codes on HTTP responses from the OSB proxy?

I tried modifying the $outbound (in ./ctx:transport/ctx:response/http:http-response-code), but there's nothing in $outbound when I go to edit it even. I do not even know if this is the right track of how to get the OSB to modify the HTTP status code.

Thanks.
Jason