I have configured OpenVPN for pfsense with all rules, etc.
OpenVPN connects me to pfSense, assigns IP address, forces all traffic on my PC to go through VPN tunnel - working like magic.

Except one thing.

when I am trying to access WebGui of pfsense it gives me 400 Bad Request error.

Used pingplotter to ping pfsense and network - I can ping it, it shows the trace, I am in the network behind pfsense, but still I cannot access Webgui due to this problem.

I was trying to access it by domain or IP - same error.

When I connect to via TeamViewer then I can access webgui without issues - but that's not solution I aim for.

I have also configured with the same settings another pfsense in different location (different country), and everything works as supposed to.

Have also tried some tips I found on forums, but nothing did help so far.