Description of the error code "ErrorUnauthorized"
Type: Configuration error (You are often able to resolve this type of error.)
The error can happen in multiple scenarios, please see below
ErrorUnauthorized when connecting the service account:
The error can happen when connecting the service account (Basic authentication)
Please check that the Exchange version selected is the correct one (Exchange 2013 is not the same as Exchange 2013 with Service Pack 1).
Please make sure that the Service Account is created with a valid mail inbox, as this is used for verification purposes.
Please enter a valid set of credentials. Check that the specified username and password can be used to log in to Exchange. If the error persists, try typing the username without the "@domain.com" in the e-mail field.
You can also check that username and password can be used to log in to your EWS URL (If you are using O365 the EWS URL is by default: https://outlook.office365.com/EWS/Exchange.asmx)
Furthermore, you can check if the service account can access EWS externally using the Microsoft Connectivity Tool website.
ErrorUnauthorized in Add-ins/Displays
The connection does not have access to the mailbox/mailboxes added to the meeting. The connection to Exchange is set-up with basic authentication (username/password). If the connection does not have the correct credentials the add-ins will fail load with the error message ErrorUnauthorized. Please make sure that the service account credentials are correct by going to Connect in Admin Center, press edit, and then update the account without doing any changes to test if the credentials are valid. If the update fails with ErrorUnauthorized Please check the solution presented above. If the update is successful see below.
The service account will try to look-up the meeting room added to the meeting when opening the Add-in. In the case where the service account does not have access to the meeting room mailbox, ErrorUnauthorized will also be shown. Please ensure that the mailbox is within the scope of the service account access.