Sophos XG - Site to site VPN - Branch office behind NAT

Hi Guys

i really need some help here.

i have tried everything, looked at every article, every KB i could find with no luck.

i have a head office and a branch office. the branch office is behind a top level firewall (behind NAT)

i am trying to create a site to site vpn but whatever i do - i cannot get a connection.

if someone has already achieved this and can share a guide or something,

that would be great