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One way to resolve this issue is by re-consenting on the myday office 365 app itself on Azure. Elveio guide - https://collabco.elevio.help/en/articles/154
Look for the myday O365 apps in Enterprise apps and click on it.
Go to permissions and grant consent. This will reset the tokens for all users
Access Permissions - Check if the account receiving the error has a shared mailbox with multiple users. Best to check calendar permission and remove the duplicate user entry.
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