actually no, this might happen due to the previous issue you had.
The FQDN is still pointing at the IP of your other PBX machine and it does not match with the IP if your current machine.
Please ensure the other VM is offline/deleted and reboot your Raspberry to update its public IP.
If you do nslookup yourfqdnhere.3cx.co.za 8.8.8.8 then you should see the same IP as the PBX machine public IP. If not, then you will get 5.7.0 Denied