Only able to connect to Wireguard peer after I ping the server

I have testing WireGuard in a home lab and I found the same problem.

I have two routers, one is the default GW in destination network and another -behind NAT of GW- with WireGuard server. I even having the route to the WireGuard network in the default GW, - and pings to each host -as you say- on the destination network from the WireGuard client, I have needed to manually add the route to the WireGuard network, on the destination host manually.

It finally worked.

Theoretically, if your default router also acts as a WireGuard server. It should work without problems, but in my case, I should have done it like this.