I am working on a process that needs to have bookings posted to an O365 Outlook calendar (located on my own Outlook licensed account in test mode).  The workflow works to CREATE the original booking on the calendar, but I'm having trouble configuring the UPDATE Exchange Item activity.

Both the CREATE Exchange Item activity and the UPDATE Exchange Item activities are configured almost identical, but I want the workflow to run only one or the other.  The Create activity is working in the conditional decision that tells it when to create the booking on the calendar.  But, when the Update activity is needed (not the initial form submission, but another step along the way), the right conditional decision branch is properly activated but the Update activity gets this message:  "Exchange Item could not be found."

What am I missing?

Note, I did also put my email address in the Assign to spot that is showing a blank here (bottom right) and tried another test, but got the same message "...could not be found."