Please double-check if the Server is visible from the outside at the port 4000. In order to do so please navigate to this page, input the Server's port number and select Check Port. If everything was configured properly and Server is visible at this specific port the form will return Success as the result.
Could you please also let us know if you've tried restarting the RU Server or the server machine after adding the port 4000 (or any other custom port value) to the Communication ports list? If no then please try adding the custom port value to the Communication ports list once again and then restarting the RU Server (please see Configuration -> Service state tab) or the server machine itself and see if this helps to resolve the issue.