I'm writing a system in Python that is using the icalendar library to generate ical invites. Those work fantastically, but if I try to send out a cancellation Outlook just displays the dreaded "not supported calendar message.ics". I originally had this issue with the invite, but solved it by fixing my date formatting.
Here is the initial invite:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//myapp//myapp.example.com//
METHOD:REQUEST
BEGIN:VEVENT
SUMMARY:Weekly Review Meeting
DTSTART;VALUE=DATE-TIME:20200331T190000Z
DTEND;VALUE=DATE-TIME:20200331T200000Z
DTSTAMP;VALUE=DATE-TIME:20200325T193007Z
UID:1@myapp
SEQUENCE:0
ATTENDEE:me@example.com
CATEGORY:EVENT
CLASS:PUBLIC
DESCRIPTION:bla bla
LOCATION:Webex
ORGANIZER:donotreply@example.com
PRIORITY:5
STATUS:CONFIRMED
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:REMINDER
TRIGGER;RELATED=START:-PT15M
END:VALARM
END:VEVENT
END:VCALENDAR
And then the cancellation:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//myapp//myapp.example.com//
METHOD:CANCEL
BEGIN:VEVENT
SUMMARY:Weekly Review Meeting
DTSTART;VALUE=DATE-TIME:20200331T190000Z
DTEND;VALUE=DATE-TIME:20200331T200000Z
DTSTAMP;VALUE=DATE-TIME:20200325T193011Z
UID:1@myapp
SEQUENCE:1
ATTENDEE:me@example.com
CATEGORY:EVENT
CLASS:PUBLIC
DESCRIPTION:
LOCATION:Webex
ORGANIZER:donotreply@example.com
PRIORITY:5
STATUS:CANCELLED
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:REMINDER
TRIGGER;RELATED=START:-PT15M
END:VALARM
END:VEVENT
END:VCALENDAR
The same code generates both and sets the METHOD and STATUS differently (DESCRIPTION also differs). I send a SEQUENCE of 0 for the invite and 1 for the cancellation. The UIDs are always consistent between the matching pair. What am I missing?