After initial VPNext server configuring according to the manual that came with the e-mail, set connection of your OS:

Windows - How to set up L2TP / IPSec VPN

Apple - How to set up L2TP / IPSec VPN

Android - How to set up L2TP / IPSec VPN

Routers - VPN set up

Soft for VPNext

Initial VPNext server configuring