Without more details (such as Duplicati version, operating system, etc.) I can’t tell for sure what is going on for you but there are two possibilities that come to mind:
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Microsoft is shutting down their current / old API. If you’re using a newer canary build (sorry, I’m not sure which one) then you may need to re-authorize the destination with OAuth via the “Graph API” (Can´t connect to Onedrive Business since a few days & Backup run through web interface does not work, but works through exported command line).
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At least one user has reported problems with OneDrive since the Windows 10 April 2018 update (OneDrive backups no longer work after Windows April 2018 Update).