Hi, after three whole days I give up.
I read all the possible solutions and setup help pages, watched YouTube, all to no avail.
And before I throw away my Synology I would like the golden tip from somebody
I did install Synology Calendar (new package, so no WebDAV/Caldav) and installed DAVx5 and aCalendar+ on my Android phone.
I do see my Synology calendars in aCalendar+ and the agenda entries I make on my phone show up in my Synology NAS. Great!
When I delete entries on my phone, they are deleted on my Synology. Great!
HOWEVER : when I make a direct entry in my Synology agenda, NOTHING happens in aCalendar+ on my phone!!
And when I delete an entry on my Synology, nothing happens either in aCalendar+ on my phone.
Those changes become visible only after activating MANUAL synchronizing in aCalendar+.
Anybody an idea what can be the reason for that?