1. Check if FQDN function is properly enabled and connected to tunnel server successfully in PBX.
Path: System - Network - Yeastar FQDN.
2. Check if Country/Region IP Access Protection is enabled by mistake, in this case only possible to disable it from local network.
Path: Security - Security Settings - Allowed Country IPs.
For second case, it's possible to verify it by checking response in browser(Google chome is recommended).
a, Press F12
b, Try to access FQDN domain
c, Go to the path in attached image to check the response
d, If you see similar response in your browser, Country/Region IP Access Protection is enabled in PBX