I'm not expert with VPS, but for first steps, I'll look closely at this:
IB-Gateway configuration:
- Make sure that your system has all permissions to use needed ports
- Add as Valid IP Trusted address the VPS machine IP address
- Select the box "allow connection from localhost only"
At NT7 side:
- Besides to add same valid IP address, I'd put "localhost" where HOST (Optional) box
If neither of this works, contact VPS support with this post info configuration
Good luck