I have setup SSL VPN for a customer but they are having issues connecting from some locations and others it works.

I have just tested on one computer that would not connect and found the following:

NOTE - The SSL port has been changed to 4433, TLS 1.2 only enabled and the user was connecting via Android hotspot.

The VPN client doesn’t connect with an SSL error and the Draytek logs show the following errors:

Receive SSL VPN client connect Version: 1.0; Go SSTPv1
Receive SSL VPN client connect Version: (null); Go SSTPv0

If I browse to the Draytek public IP on port 4433 via a web browser I get a certificate not trusted error and when I click proceed to webpage it doesn’t load. If i click certificate details it says Draytek so it must be hitting the router. I have tried disabling the firewall but didn’t make any difference.

I have verified the VPN works from my computer and others have successfully connected.

Draytek 2862 running v3.8.9.2 and Smart VPN v5.0, client is Windows 10

Any ideas on what is causing the issue?