I'm using a Fritz!Box in Client Modus behind an OpenWRT Router. On my Android phone I'm using Fritz!App Fon to use the phone functions of the Fritz!Box. This runs normal when my Android phone is in the same network zone as the Fritz!Box and OpenWRT (192.168.10.0), which is LAN zone.
But when I connect from outside via Wireguard from the Wireguard zone 192.168.9.0, the Fritz!App is connecting, I can even access my phone books on the Fritz!Box, but the telephone state never switches to green, that means it doesn't allow me to make a call. For what ever reason it looks, that SIP packages are not going from the Fritz!Box to the Fritz!App phone or vice versa. The funny thing is, that I can reach each LAN client from wireguard zone and each LAN client can reach the wireguard clients outside.
I already add the entry option helper 'sip' to the wireguard zone in the firewall settings as mentioned in a previous post in this forum, but there is no change.
Does anyone has an idea how to solve the issue?