In iOS, Select L2TP VPN type;

In Android Jelly Bean 4.x system, Select L2TP/IPSEC PSK mode, not: leave "L2TP secret" and "IPSec identifier" fields empty;

In Windows7/Windows8 OS, when creating the VPN connection, remember to check the "Don't connect now; just set it up so I can connect later" option, then from the Option tab of the VPN connection, select "L2TP/IPSec" type, check "Allow these protocols" checkbox, use MS-CHAP v2, and in Advanced settings, fill "freel2tp" in the Key field;

Video - How to setup L2TP Free VPN connection in Windows 7 (remember to replace the server IP, username, password and secret field with the values we shared on our home page)