Under normal circumstance user behind the WIFI network can easy connect to SDN-VPN server from anywhere in the world, however, under special condition the connect attempt fails. Possible failures are caused by below situation,
1) Home / Office WIFI network does not support VPN Pass-through, that does not allow TCP/UDP VPN protocols.
2) Home / Office WIFI network restricted (banned) outgoing target server location, such as "sdn.cowbee.net".
3) At last, obviously input invalid username and password are 99% of the problem.
Look that helps! Good luck!