Raspberry pi, wireguard and gateway problem

[elgringo]

Hi!
I have gone from pfsense to opnsense because of the support of wireguard. Now I have some problems.
I have every device behind the opnsense firewall routed trough the wireguard vpn.I have a raspberry pi that I want to route trough the default gateway so it gets my external ip so I can access it from the internet.
I made a rule that looks like this.

Interface: LAN
Source: 192.168.1.20 (ip of the raspberry)
Gateway: WAN_DHCP:93.233.54.1
The problem is that it is not getting any connection with the internet. If I change the source to my desktop computers internal ip, the desktop computer gets the external ip instead of the wireguard vpn ip. So the rule works for my desktop computer but not for the raspberry pi.

What am I missing? Any suggestions?