Hi @davebenton,
This is a Microsoft-specific message, so it is strange they they are saying they cannot find your account.
Are you able to login to the account outside of the odrive flow?
Usually when linking an account with odrive, Microsoft will direct you to the proper OAuth login after inputting the Microsoft user name.
Can you provide a screenshot of what you see when you first try to link the account from odrive and it redirects you to Microsoft?