Calendar Import failed, how to find out why?

Importing an ICS file I get “Import partially failed. Imported 0 out of 1.”

Is there a log that can tell me what is causing the failure?

This forum post suggests some random website with a validator but I don’t want to do that.

In this case you have two options

  1. search a CalDAV validator which you can install on your local PC/server.
  2. read the CalDAV documentation and check each line of the CalDAV file on your own.