If your Microsoft 365 Calendar Provider is Offline or you face issues with Unauthorized or resource calendar does not exist statuses, please follow the check list below if you have integration ready for your account.
Microsoft 365
Does your Service account have an Exchange online license?
The service account requires a license for Microsoft Exchange Online. You can check that at your Microsoft 365 Admin center.
Do you have EwsApplicationAccessPolicy configured in your Microsoft 365 tenant?
If so, check if the MeetingRoomApp is in your Allowlist. More information about Microsoft 365 policies you can find in the Microsoft Documentation.
The service typically takes less than 30 minutes to provision a user or to sync changes for a user. It could take up to 24 hours for provisioning to occur or for changes to sync, more information in the Microsoft Documentation.
Does your account have Full Access permissions to your resources?
You can configure (adjust) them using steps in this article.
Have you changed a password recently or the password has expired?
The calendar provider can be disconnected (offline) if you change a password or disable MeetingRoomApp access. This can be solved by reconnecting your Calendar Provider in your account..
Have you made any changes in your Microsoft 365 account?
The service typically takes less than 30 minutes to provision a user or to sync changes for a user. It could take up to 24 hours for provisioning to occur or for changes to sync, more information in the Microsoft Documentation.