Why is my Web API with Application Permissions to Bookings.ReadWrite.All unauthorized when querying Graph API Bookings endpoints

Question

We are building an API to get and update Booking Appointments using Microsoft Graph API and application permissions.

We have registered an app in Azure, added the Bookings.ReadWrite.All application permission and admin consent has been granted.

When we query the endpoint with application permissions we receive an Unauthorized error, but if we query using delegated permissions, as a user who is a member of the Bookings Calendar, it's fine.

var result = await _graphServiceClient.Solutions.BookingBusinesses[_BookingCalendarId].Appointments[appointmentId].GetAsync();

We have queried Appointments, StaffMembers and Services all with the same result.

We're constructing our Graph Service Client this way:

    public AppGraphService(IConfiguration config)
    {
        _config = config ?? throw new ArgumentNullException(nameof(config));
        _client = new Lazy

Answer 1

Hello Steven Bitaxi,

The error is because you have granted Bookings.ReadWrite.All , but to access /appointments endpoint you also need to grant BookingsAppointment.ReadWrite.All application permission to the Microsoft Entra ID application.

Hence to resolve the error, grant BookingsAppointment.ReadWrite.All application permission too:

I generated access token using client credential flow:

GET https://login.microsoftonline.com/TenantID/oauth2/v2.0/token

client_id:

client_secret:

scope: https://graph.microsoft.com/.default

grant_type: client_credentials

Make sure BookingsAppointment.ReadWrite.All role is also present in access token:

Now I am able to call the Get booking Appointment API successfully:

GET https://graph.microsoft.com/v1.0/solutions/bookingBusinesses/******@xxx.onmicrosoft.com/appointments/AppointmentID

With Bookings.ReadWrite.All role only I got 500 error:

Hope this helps!

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