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You are posting in international section
So don´t be suprised, when your answer will be in english

I never tested this case over WAN.

Here is another Topic:

Installing STUN / TURN Server

I’ve no issues with getting video calls to work within the LAN. But calls that cross over into other networks just don’t connect - the spinner just keeps spinning forever. This must be because firewalls / NATs are getting in the way of making a peer-to-peer connection. Thus, I need to run a STUN / TURN server. So I’ve installed “coturn” and I’ve gone through the options in “turnserver.conf”. I have a static public IP address. I’m using the standard port 3478 and have opened the firewall ports…

Its about installing TURN Server

Another tut.:

Setting up a TURN Server for Nextcloud Video Calls

cheers