MailboxNotHostedInExchangeOnline error during calendar access

Question

I'm seeing this exception MailboxNotHostedInExchangeOnline from an MIT (educational institution) Outlook account that we're trying to connect to in order ho to access their calendar events (https://graph.microsoft.com/v1.0/me/calendars API), but there's not much additional information online about what this exactly means

  "error": {
    "code": "MailboxNotHostedInExchangeOnline",
    "message": "Mailbox is hosted by an on-premises or non-Exchange server, which is not supported.",
    "innerError": {
      "request-id": "REDACTED",
      "date": ""
    }
  }
}```

Is this a relatively new addition to the API? If so, does anyone have ideas on how to circumvent this?