Our Cpanel servers have CSF installed by default, which is why it is possible that it may block one of your clients at some point. The main reason for blocking is usually due to failed access attempts. That is why in the following tutorial we will explain how to unblock and add your client's IP to the whitelist. To do this, first we need to know the client's IP, in the case that it has a dynamic IP, it is better to add the entire range "in case it is trustworthy."
Once we have the range or IP, we must access our WHM panel.

Once inside, we go to Additional Programs and within this, ConfigServer Security & Firewall.

Once inside the Firewall, we must look for csf - Quick Actions and in Allow IP address we must write the range or IP and click on the Quick Allow button.

Once added, a page will appear indicating that the IP has been added to the whitelist, in the case that it was blocked, it would also indicate it to us.