hey @mariog123,
welcome to the forum.
sometimes it would make sense to search the forum first… and find several threads covering your question. maybe like this one --> Nextcloud Talk documentation? (and many more!)
here’s a quick summary… if you’re running the default setup that’s delivered with the installation of the app you most prolly won’t be able to make videocalls outside your lan.
if you want to run this feature you need to install your own co/turn-server somehwere…
best of luck
jimmy