How to set up IIS and VPN access?

Question

IIS

Hello.

There is 1c which is published via IIS to a domain of the form 1c.site.ru.
For security, I want to make it accessible only from 1 IP address (IP address of the Internet where the server is installed).
I made VPN access with this IP address, but IIS does not allow connecting to the site, it says access is denied, although everything works fine from the internal network. Through 2ip I check everything is fine, the IP that is needed for access.
Tried both PPTP vpn and OpenVpn the result is the same. IIS somehow understands that I am connected via VPN and I have a different IP that is not allowed in IIS.
If I add the IP of the remote Internet, then everything works fine, although it is connected at that moment via VPN.
I don’t understand how to make it so that, when connected via VPN, you can go to a site published in IIS with one allowed ip ...