★Test the free Version first, if something doesn’t work there, it won’t work in the Pro Version.
★Please note that I did the best for providing a good CalDAV support, including a large number of various tests, but there may be still some bugs and I am not responsible for any appointments you missed due to wrong synchronisation.
★If you used the CalDAV feature of iCal Import/Export CalDAV prior Version 2.4v103, please drop and recreate your CalDAV synchronisations, as there where many bugfixes regarding exclusions and recurring events.

Following iCalendar properties are not supported, if you change events locally and you sync your phone, those properties get lost:
★ATTACHMENT
★Probably some others, who knows.

The following providers are supported and also tested:
★iCloud
★fruux
★owncloud
★baikal
★Posteo
★Gmx
★Web.de
★Synology
★There may be also support for all SabreDAV based CalDAV clients, but they are untested

There is no support for the following providers as the are not providing the CalDAV features the app needs:
★mailbox.org
★Yahoo
★memotoo