Enable DAV daemon over WHM –> Service Manager
Remove if needed from disable features WHM –> Feature Manager
Allowing ports 2077, 2078, 2079, and 2080 in your firewall
If CSF update csf.conf TCP_IN with the ports range 2077:2080:
/etc/csf/csf.conf
TCP_IN = "20,21,22,25,26,80,110,143,443,465,587,993,995,2082,2083,2086,2087,2095,2096,2077:2080"
Restart csf
csf -r
cPanel's documentation:
https://documentation.cpanel.net/display/CKB/How+to+Set+Up+Calendars+and+Contacts