You back up Office 365 mailboxes with Acronis cloud agent.
After you've navigated to Microsoft Office 365 in the backup management console and clicked Refresh, you notice this warning message in Activities:
Cannot connect to site 'SPO root'.
Issue in the product.
The warning appears if there is no SharePoint Online quota under user’s account. It does not impact product functionality and can be safely ignored.
The issue has been fixed in Acronis Cyber Cloud 8.0, please update to the latest build.