On attempting to create a new backup set for any of the M365 services (Exchange, OneDrive, SharePoint or Teams), the user encounters the following error:
This can happen to users who do not have any OneNote notebooks.
The Redstor web app requires permissions to the OneNote API in order to protect M365 data. Although OneNote is included in all M365 Business plans, the OneNote service is not auto-linked to a subscription as is the case with Exchange, OneDrive, SharePoint, Teams and Skype. This error will therefore occur even if no user in the Microsoft tenancy has accessed the OneNote service.
To link the OneNote service to a subscription, a user (any user in the relevant tenancy) must log into OneNote, either via the desktop app or via the OneNote web app. It is not necessary to create a notebook or take any further action. Once the service has been accessed, the user will be able to create backup sets and authenticate without encountering the above error.