Need admin approval while logging in Smartsheet

When the free users try to log in Smartsheet via with Microsoft company account, some of them gets this notification.

"Smartsheet needs permission to access resources in your organization that only an admin can grant. Please ask an admin to grant permission to this app before you can use it."

Who is this admin? The system admin of Smartsheet? Or the IT of my company who controls Microsoft permission? How to give the free users access?

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