Icalendar ICS update not working in google calendar

Question

I have some trouble with the ICS attachment to Gmail/Google calendar addresses. When I have to edit an event I send an update by mail with an ICS file with the same UID of t

Answer 1

Some of the answers provided are not (entirely) correct.

In short, 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-GUESTS=0:mailto:recipient@gmail.com

I had the same problem and to find the answer I:

1. Sent myself an invitation using Google Calendar itself + an updated invitation
2. Compared the two .ics files
3. Ran many different self-generated variations on those two .ics files to find out which parameters were really necessary

These are my findings:

• Increment SEQUENCE from 0 to 1 (or further if you want to update updates)
• METHOD has to be REQUEST (*1)
• Email sender does NOT need to be the same as ORGANIZER (Sidenote: It is however, not possible in Google Calendar to update an ORGANIZER)
• ORGANIZER does NOT need to be listed as an ATTENDEE
• Email recipient has to be an ATTENDEE
• Also (as mentioned above), the ATTENDEE needs additional parameters, not just :mailto
• STATUS does NOT need to be provided. EDIT: This is the case when sending invites to google calendar / chrome / mac, but the invite doesn't get a proper preview in other combinations it seems
• Arguments that take several lines in the doc should be indented by one space on the next line
• In iCalender objects generated by Google Calendar you may notice that lines that are too long are broken into several lines into the document, however this is not required (e.g. you can provide a description that is a very long string, just make sure it only takes one line or cut it in lines where every line is indented with one space)
• Bonus Tip: Use same UID in original invite and update (this is actually not required BUT makes sure your historical test results remain unaffected...)
• Bonus Tip 2: for easier testing, also change the SUMMARY and subject of your email each time

Cleaned up example:

BEGIN:VCALENDAR
PRODID:-//YourCompany/AppName//EN
VERSION:2.0
CALSCALE:GREGORIAN
METHOD:REQUEST
BEGIN:VEVENT
DTSTART:20180331T150000
DTEND:20180331T160000
DTSTAMP:20180331T150000 // make sure to populate this dynamically
ORGANIZER;CN=organizer@gmail.com:mailto:organizer@gmail.com
UID:BESTIDEVER123
ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=
TRUE;CN=Recipient Name;X-NUM-GUESTS=0:mailto:recipient@gmail.com
CREATED:20180331T150000  // make sure to populate this dynamically
DESCRIPTION:Best event evah
LAST-MODIFIED:20180331T150000 // make sure to populate this dynamically
LOCATION:
SEQUENCE:0 // don't forget to increment this!!
SUMMARY:A Wonderful Event
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR

(*1) The only question that I could not figure out is how to have a METHOD:PUBLISH that can be updated - I am trying to make a calendar publishing app that should NOT take replies. If anyone can figure that out I would be very grateful. :-)