You also need to register for the specific service. For more info:
http://www.gsis.gr/gsis/info/gsis_site/News/news_0095.html (Greek only)
After you have registered for the service, you can use our app to make your searches.
For more details, see the help page in the app.
If GSIS goes on with upgrading its infrastructures (on 5 Dec 2016) for supporting only the TLS 1.2 protocol, then he app will probably not work on devices with operating system older that Android 4.1 (Jelly Bean - Api 16). The reason is that these OSes do not support the TLS 1.2 protocol.