How does VPN server work on ASUS RT-AC68U gray IP router?

Question

Asterisk

The ASUS RT-AC68U router comes standard with a vpn server.
It starts in a couple of clicks, after which it generates an *.obpn file for the client by clicking the button.
But my ISP issues a gray IP and the *.obpn file is automatically bound to this gray IP. As a result, you can't reach him. I reserved an external static white IP from the provider, opened *.obpn with a notepad and changed the value of the "remote" line from gray to white - it does not work. How is it decided? I'm not an IT specialist, I can't draw complex schemes.

Answer 1

chan_sip.c:26407 handle_request_invite: Call from '' (185.xx.xxx.xx:yyyy) to extension '+xxxxxxxxx' rejected because extension not found in context 'public'.

If the IP address here is not yours, then this is not a mistake, these are attempts to make calls from your PBX remotely. In other words, they are trying to "hack" you.
This is a consequence of attempts to "hack" you. The PBX receives an "INVITE" connection request and tries to work with it (reject) and waits for a response from the other side. There is no answer, she again tries to inform the remote side of the information, again there is no answer. As a result, a timeout occurs and the asterisk reports this to the log.
If a