Why is the PBX not available from the phone?

Question

Computer networks

Good day!
Router ISR 4331
External IP dedicated for telephony 1.1.1.1
Telephony server 10.0.0.10
Translation is configured on the router:
ip nat inside source static 10.0.0.10 1.1.1.1
3CX telephony (ports): https://www.3cx.com/docs/ ports/
Telephony is available for PC outside the network (Web panel opens, desktop application works), but not available for phones (Both panel and mobile application), but when connected within the network, access appears, the site and application work. What could be?

Answer 1

1) IP 1.1.1.1 refers to external networks, the subscriber must be allowed external connection. In its Options tab - see Disallow use of extension outside the LAN
2) Look in 3CX itself - settings / network settings - if the range of internal addresses and external address (1.1.1.1) is correctly selected
3) In the Phone Provisioning tab - look at the settings for the application subscriber, what is there with the Provisioning Method settings in the IP Phone section.
4) If the application works fine and calls, then all the settings are made correctly, it just uses its own 3CXTunnel.

Answer 2

https://www.3cx.com/docs/manual/firewall-router-co...
Did you do everything according to the manual and turn off SIP ALG?