What should I do if I cannot access my CyberPanel login account in below scenario?

When attempting to reach my panel, It encounter the error message “This site can’t be reached panel.demo.com took too long to respond.” This issue occurred after interacting with CSF (ConfigServer Security & Firewall) and attempting to refresh it. Since then, I have been unable to access my panel, and every time I try, the same error message appears. How can I resolve this problem?

SSH into the server.
whitelist your IP

csf -a

replace with your public IP address
Try logging in.
It could be that you closed the port and your IP address has changed.