Currently there is no such API to update the Email subject/body this is by design, The API you are trying is to update the messages .
The meeting request has already been sent and might not be updated. (ErrorSentMeetingRequestUpdate)
Idan Gazit
21
Reputation points
I am using the PATCH MS Graph API to modify the email subject/body and I am getting the following error:
"The meeting request has already been sent and might not be updated. (ErrorSentMeetingRequestUpdate)"
I noted that it appears in emails of calendar invitations...
Can you please give some more details of this error, when it happens and how we can avoid it?
Thanks