I am new to FreePBX and am starting to learn and configure it but messed up the FW. Now I can’t access anything and can’t shut it down in a Terminal window. Would anyone know how to reverse what I did so I can go back to step one in the configuration?
Reboot it, you’ll have a few minutes to get back in and sort.
I wrote this a few months ago 
Getting locked out during the initial setup of FreePBX affects even the best of us, but of course we very rarely admit to it…
If it wasn’t your antivirus getting a little lively, then it might be one of these:
For an IP, remember http://
HTTPS relies on certificates, which are usually tied to domain names rather than IP addresses. Certificate Authorities, such as Let’s Encrypt, rarely issue them for IPs at all. When your web browser connects to https://123.45.67.89, it almost always finds one of three things: no certificate, a self-signed certificate, or a certificate valid for a hostname that doesn’t match the IP. Any of these might fail modern security checks and block the connection.
Ctrl+Shift+Del the cache
When an install crashes or Apache restarts mid-request, your web browser can hold onto broken or partial responses from before the server has fully recovered its normal working state. Those cached copies keep getting served back to you over and over, making it look like the problem is still there when it isn’t. Clearing the cache forces a fresh pull from the server, and this is usually the fastest and most reliable way to tell a real issue from a phantom one.
Reboot your way back in
If the firewall has locked you out during setup, rebooting the server can give you a short window on boot before it starts blocking you again. You get just a few minutes, but it’s enough time to reach the GUI or SSH from the same IP that got blocked, mark it as trusted, and carry on as you were. This is a safe and typical way back in when switching to an alternative IP isn’t an option, and avoids having to go the long way around just to re-establish access.