Cannot connect to OPNsense firewall over VPN

[seamus]

[EDIT]: I've made some forward progress, so I'm updating this post.

I've got my OPNsense+OpenVPN configured, and **mostly** operational now, but there's one awfully annoying item that persists:

The remote LAN is in the US behind an OPNsense firewall that also serves as the LAN gateway, DNS and DHCP server. Its IP address on the LAN side is 192.168.1.1.

My local network is behind a P.O.S. Sky router in the UK, which was configured by someone else - I am using the network here as a guest - not as the admin, tho' I might be able to get a change made if it would help. The P.O.S. Sky router's LAN interface is also 192.168.1.1, but it does not respond to https:, only http.

I can reach all the active hosts on the remote LAN as long as I know its IP address. That's not a huge problem as it's a small network, but still - it would be nice if that worked. The exception to this is the one I really need to access: the OPNsense firewall at https://192.168.1.1  If I just connect to 192.168.1.1, I am connected to the P.O.S. Sky router. When I specify https://192.168.1.1, it simply refuses to make the connection (I assume due to the duplicity of the single IP address.

I'm currently working around this by making a remote desktop connection to a host on the remote network, and connecting from there, but that's awkward, and since it's a Windoze PC, it may fall over and die at any moment!

Can anyone tell me how to resolve this? I need access to the OPNsense firewall on the remote LAN - not the P.O.S. Sky router here on the local LAN.