Hey there,
when trying to import an .ics Appointment file via Caldav (for example in Thunderbird, where the Calender is added via Caldav), specific UIDs (for example: "UID:flexperto/mlpfinanzberatung/prod" doesn't work, but "UID:flexperto/mlpfinanzberatung" works fine) specified in the .ics file will result in an 404 error, screenshot attached.

The error message of thunderbird is: (German)
"Status-Code: 2147500037, Die Anfrage kann nicht verarbeitet werden.

Server Replied with 404"

I get the same error (404) when importing the .ics file with my smartphone. There i can import the .ics in my aCalendar app, but when the OpenSync App tries to synchronize the calendars via Caldav, it gives the error message 404 for this specific appointment.

importing the .ics with the SoGo Webinterface works just fine