Talk works correctly only in the same network. To work with multiple client behind NAT, TURN server is required.
Official NC HowTo for installing TURN server: https://help.nextcloud.com/t/howto-setup-nextcloud-talk-with-turn-server/30794
Dockers with coTURN server:
Online verificator for public TURN server:
Some found HOWTOs:
--min-port Lower bound of the UDP port range for relay endpoints allocation. Default value is 49152, according to RFC 5766. --max-port Upper bound of the UDP port range for relay endpoints allocation. Default value is 65535, according to RFC 5766.