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First, I need you help me to check the permission roles of that account, to see if the error show direct. Please login to Admin Center: admin.microsoft.com -> User -> Active users -> Select the affected user -> on the pop out Windows, click on Roles: ensure the roles already assigned.
Sometimes it happens as the user has too many roles.
Also, if you see the error shows "Access denied" or "Tenant block", I suggest you raise a support ticket from the Microsoft 365 Admin Center, where the Exchange Engineer team can perform a remote session to investigate the situation, verify the backend configurations, and run any necessary synchronization tools to resolve the problem. It could be saving your time if the workaround I send above does not work.
Reference: Get support - Microsoft 365 admin | Microsoft Learn
Note: To create a support ticket, you need to have Microsoft 365 admin privileges and if you aren’t admin of your organization, please contact the admin of creating a new ticket.
Apologies for redirecting you to the related development team support as the moderators in this community have limited resources to check the backend information, and to get the fast and better assistance we requested for it.
Appreciate your patience and understanding.
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