Microsoft 365 backup fails with error: Access to this site has been blocked. StatusCode: 423

Symptoms

Backup of a Microsoft 365 account fails with the error message:

CONFIG_TEXT: Access to this site has been blocked. Please contact the administrator to resolve this problem.
StatusCode: 423

Cause

Microsoft's GraphAPI has blocked this account's OneDrive or SharePoint access. The account might be unlicensed or archived for being unused.

Resolution

Solution 1:

Assign a license to the user that grants OneDrive access.

Solution 2:

Exclude the OneDrive or SharePoint site from the Protected Item. For more information, see:

• Configuring selections | Microsoft Office 365 | Comet Documentation