Login to SolusVM panel, select VPS, click manage,  settings, turn on TUN/TAP and restart VPS.
Run this command to verify if TUN/TAP is working or not.

$cat /dev/net/tun/

If the output isn't like the mentioned below, it means TUN/TAP is not working.

Output:
cat: /dev/net/tun: File descriptor in bad state