Hi Edwin,
It appears that you were still on the old OneDrive authentication method.
A few months ago, we changed how UpdraftPlus authenticates with OneDrive by default, which does not require a custom OneDrive app.
Sites using the existing method should not be affected, and the existing method should still work.
However, it is possible that something has changed on OneDrive’s side. I will forward this to our developers for further investigation.
I’m afraid that any backup files already stored on the server will need to be removed either via FTP, or by deleting the backups in question via the Existing Backup tab.
Apologies for the inconvenience.
Best Wishes,
David N