Reach WireGuard client from server network

[murmelbahn]

Hi all,

I have a little problem with my WireGuard setup. All my clients are connected to my OPNsense Server and can access everything on the OPNsense side. I have one Debian client which I want to access from the OPNsense side.
Sadly I don't know how to archieve this. Basicly I want to use the VPN to "both" sides.
Can someone give me a hint how to configure this? When I try to ping the VPN IP of the Debian client (100.65.1.2) from the OPNsense it does not send the packages through the tunnel.

€: Has to add the VPN Network (100.65.1.0/24) to the allowed IPs of the client.