https://together.jolla.com/question/...ts-explicitly/ lists the problem. See my follow on comment about setting the parameters which is how it worked on the N9 also.

Really though, I'd like to see iCloud as a first class account like Google is accessed in accounts or failing that listed explicitly like Yahoo or Memotoo is listed in the CalDAV list without the need to hack in the server or special principal number. There are iCloud plugins on Android that avoid that configuration with a user just using their AppleID email address and password so it is possible to make it really simple and would make Sailfish integration with the Mac/iOS world so much better.