wireguard Opnsense routing

[m4rtin]

Hallo,
my opnsense (a) has a wireguard peer that is another opnsense (b).
Now I want that any LAN device from opnsense (a) can access a device in the LAN of opnsense (b).
I added the LAN (b) in the Allowed IPs of the wireguard peer in opnsense (a).

So in my opinion the opnsense (a) should now know that packages to (b) should go through the wireguard tunnel, because it is defined in Allowed IPs. But for some reason in the live view the ping was send to the WAN interface.

Do you know what's missing?