The server url should be protocol://hostname:port (if different port than 80)
Please check that the server is visible from the client, often firewalls prevents users from accessing.
A tip is to use Sense in the browser http://localhost:4848/hub/my/work
and then open the JS console (F12) to see check why connection fails.
After install, make sure you can login in to the server. Do this login also from a client computer where you want to run QGA not just on the server. It's essential that the map server is visible form the client.
If this works the url to the server is http://myserver
This type problem is normally due to that the right ports to server has not been opened.
If you for instance install the map server on port 81 because port 80 (normal http traffic) is occupied, then port 81 must be opened in the firewall and accessible from the client. Test using
If this works the url to the server is http://myserver:81