Get working config only if public IP is entered instead of Dyn URL

I get a warning “i” in Talk App Settings when entering my.turnserver.domain:3478.

Giving my.public.IPv4:3478 then i get a tag that it’s working.

My Router has opened port 3478 UDP and TCP and forwarded to the turnserver.

My nextcloud server is working behind the same router and behind a reverse proxy because i have different services using port 443 (cloud, mail, …)

My turnserver URL ( isn’t routet through my reverse proxy. At DynDNS my points to my public IP adress.

Can anybody help me with that, what’s wrong?