Hi Peter,
If I'm reading your question correctly; what you are requesting is to modify the Access Control List for nginx's HTTP (Port 5000 by default or 80 if you used that when setting up).
What needs to be done is either remove the 'deny all;' line in that config file or add your static IP to the list to allow HTTP traffic.
If you are on windows you could use WinSCP to SCP to your Linux instance, navigate to that file and WinSCP will allow you to edit the file and save it directly back to the Linux instance.
The section you are looking for is around line 82 called 'server {' under that you will see the following section:
Code:
allow 192.168.0.0/16;
allow 172.16.0.0/12;
allow 10.0.0.0/8;
allow 127.0.0.1;
allow ::0/0;
deny all;
Modifying this is not officially supported by 3CX, so keep this in mind.
The most secure method will be to add another 'allow' line which has your sites Public IP so you are not opening HTTP to the entire world. If you cannot do this, then you can remove the 'deny all;' line at the end and the firewall will allow unrestricted access to the HTTP server externally.
Again, be aware there is a reason HTTP is restricted to internal subnets only, so make the changes at your own risk.