How to update ICS calendar meeting?

Question

I am trying to generate .ics files which I want to send as attachments to customers. For some reason, if meeting is rescheduled, it is not updated neither in google calendar nor in Calendar app on mac OS.

Here is a meeting.ics with SEQUENCE:1:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//example.com//Appointment v1.0//EN
METHOD:REQUEST
BEGIN:VEVENT
UID:citfslfcd0001hx61sjcqqp4q
SEQUENCE:1
DTSTAMP:20160923T151743
DTSTART:20160923T211500
ATTENDEE:;CN="user1";RSVP=FALSE:mailto:[email protected]
ATTENDEE:;CN="user2";RSVP=FALSE:mailto:[email protected]
LOCATION:Sweden
DESCRIPTION:Meeting
SUMMARY:Meeting
CLASS:CONFIDENTIAL
CATEGORIES:BUSINESS
END:VEVENT
END:VCALENDAR

And here updated meeting with SEQUENCE:2 and DTSTART one day later:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//example.com//Appointment v1.0//EN
METHOD:REQUEST
BEGIN:VEVENT
UID:citfslfcd0001hx61sjcqqp4q
SEQUENCE:2
DTSTAMP:20160923T161267
DTSTART:20160924T211500
ATTENDEE:;CN="user1";RSVP=FALSE:mailto:[email protected]
ATTENDEE:;CN="user2";RSVP=FALSE:mailto:[email protected]
LOCATION:Sweden
DESCRIPTION:Meeting
SUMMARY:Meeting
CLASS:CONFIDENTIAL
CATEGORIES:BUSINESS
END:VEVENT
END:VCALENDAR

1. When I open first file in google calendar (from email attachment) or Calendar app on Mac meeting is added to calendar as expected.

2. When I open second file in google calendar then duplicate meeting with new meeting date is created.

3. When I open second file in Calendar app then... nothing happens - first meeting just "bounces" in date cell, but nothing happens...

What might be wrong with those ics files?

---

I also can't cancel meeting despite gmail recognizes it (the .ics attachment) and shows message "This meeting has been canceled".

Here is a screenshot of what happens when I try to update event:

And here what gmail show when I try to cancel the meeting (It shows "Meeting has been canceled" in Polish) (but event is not removed / updated in google calendar):

Answer 1

Your ATTENDEE properties look wrong. The colon character that is after the property name should not be there due to the fact that the property has parameters.

For example this:

ATTENDEE:;CN="user1";RSVP=FALSE:mailto:[email protected]

should be this:

ATTENDEE;CN="user1";RSVP=FALSE:mailto:[email protected]

Answer 2

In fact, your ATTENDEE property needs more arguments to make sure Google Calendar considers it an update:

ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS- 
 ACTION;RSVP=TRUE;CN=Recipient Name;X-NUM-UESTS=0:mailto:[email protected]

I have provided a more complete explanation here: https://stackoverflow.com/a/49585109/5669260