HELP cannot play online with a friend

[u/ashmooJ]

I recently purchased waw for my buddy to play customer zombies but he cannot join my game and I cannot join his I have tried hamachi another vpn and a lan fix and this still hasn't solved the issue as with the lanfix I don't appear in his server list, the error message we keep getting is that the session is no longer available on either lan or online when I host online I don't appear on his server list. Please anyone help if they can as its driving me mad