I don't think I installed any 3rd software. The only thing close to blocking anything is iptables.
The steps are simple. I enter the ip address and press on the button. cpanel states that the address has been blocked. I return to the home page of ip blocker and the ip address is not listed.
cPanel IP Blocker won't add IPs to iptables. What it actually does is, it simply adds a deny entry in .htaccess file for the IP you entered. If you are not able to see the list of IPs you blocked, check the .htaccess file in public_html folder. Or you can add IP addresses directly into the .htaccess file, but make sure to enter them in CIDR format only.