The external address won't be shown in the application if either Sighthound Video was not requested to automatically open a port in your router, if your router does not support such programmatic port opening, or if the end to end connection could not be verified.
This does not necessarily mean that external access is not working, but that you may need to open the port yourself and you will need to look up your IP address yourself as well. You can find your external IP by typing "what is my IP" into google or visiting a site such as
http://whatsmyip.org.