MUST BE A PUBLIC IP, private IPs cannot be used for SIP trunking.
See below ranges or further explanation via URL.
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
https://wiki.teltonika.lt/index.php?title=Private_and_Public_IP_Addresses
Your production IP address will be the primary IP where we will signal and send calls to and get calls from.