How to configure free/busy calendar with Kontact

Attempting to publish free/busy calendar information from Kontact to a secure web site.
The web site is linux based and managed using Cpanel.

In Kontact: settings → configure Kontact → select Free/Busy
This brings up KOrganizer Free/Busy Configuration.
I left the retrieve page blank.
The publish page require a URL for a server, along with username and password.

I have no idea what server is needed. I set up an FTP server on the web site. That didn’t work.
I went into Cpanel, email settings. The options include a free/busy URL from the Horde email reader. This server doesn’t work either.

Any help would be appreciated.