This issue sounds like a problem with the 'firstname.lastname@example.org' user setup. Perhaps in the Azure portal.
1. Check the api permissions - if you log a support incident you'll need to provide the screenshot from azure portal.
2. Please call the api using microsoft graph explorer or postman (or another third party application) and see if you are getting correct response
3. The above error code tells that the above user is invalid or doesn't exist. Check whether the user exists in portal.office.com. If the user exists try to login as the user, test the same API call to see if it works (either using MS Graph Explorer or POSTMAN)
If you need further help I suggest that you log a support incident for this.
Please provide us with the INC number here to help us track it.
Posted: 1 month ago
Posted: 20 May 2022 3:06 EDT
Vijay Boinepally (VijayB3101)