I am using 3CX on a Raspberry Pi4-CM4 and cannot get the server to work using full cone NAT.

I have followed all the documentation to the letter but for some reason I cannot stop the router changing the ports (Port Preservation).

I have done everything i can think of. SIP ALG is turned off as required but ports 5060 & 5090 seem to be the only ports that will not map properly as they seem to map to ports in the 20000's

Any help would be appreciated.

Many thanks

Michael