Teams Rooms devices can't fetch calendar from Exchange Online

Symptoms

After you sign in to a Microsoft Teams Rooms device, the following error message is displayed:

Cannot fetch calendar

And the following error is logged in the sign-in logs in Microsoft Entra ID:

“requestId": "<request ID>",
"userDisplayName": "Teamsroom@contoso.com
"userPrincipalName": " Teamsroom@contoso.com ",
"userId": "<user ID>",
"appId": "<app ID>",
"appDisplayName": "Office 365 Exchange Online",
"ipAddress": "<IP address>",
"clientAppUsed": "AutoDiscover",
"userAgent": "MicrosoftTeamsRoom/<version>",
"correlationId": <correlation ID>",
"conditionalAccessStatus": "failure",
status": {
    "errorCode": 53003,
    "failureReason": "Access has been blocked by Conditional Access policies. The access policy does not allow token issuance.",
    "additionalDetails": "If this is unexpected, see the conditional access policy that applied to this request in the Azure Portal."
}

Cause

This issue occurs if modern authentication isn't enabled for Teams Rooms, and your organization uses a Conditional Access policy to block basic authentication.

To find out which Conditional Access policy is applied, review the Microsoft Entra sign-in events.

Resolution

To fix the issue, enable the client-side setting for modern authentication on Teams Rooms:

1. In Teams Rooms, select the More (...) button.
2. Select Settings, and then enter the username and password for the device administrator.
3. On the Account tab, turn on the Modern Authentication switch, and then select Save and exit.