How did you created the entity (object)?
When you are calling a REST service: you must have a GET service that is actually getting something from database or creating the object in memory, use export mapping to export that object and attach it to the HTTP response.
Post the Microflow that handles the GET request.
Have you added logging? If you set the log level to TRACE for REST Consume on the application making the call, and TRACE on REST Publish on the application that provides the service you should be able to see the messages being sent and received at both ends. This should help you debug what is happening.