Hello Tony,
Thanks for your question.
If the account was left in the old tenant, remove the association from the previous tenant and re-create or update the account in the new tenant.
Also, open a new in-private browser session or have the user try to access from a different browser. In this case, users must sign out from their active session, and then try to sign in again.
For this particular error, you can look at detailed troubleshooting steps here:
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Regards,
Abiola