Why is C# app unable to enroll device into MS Intune via Microsoft graph API?

I´m trying to create a C# app which will enroll devices into Intune via Microsoft graph API, but after calling graphClient.DeviceManagement.WindowsAutopilotDeviceIdentities.PostAsync(newDevice), It keeps throwing this exception:

No OData route exists that match template ~/singleton/navigation with http verb POST for request /DeviceEnrollmentFE/StatelessDeviceEnrollmentFEService/deviceManagement/windowsAutopilotDeviceIdentities."} Microsoft.Graph.Models.ODataErrors.ODataError

First of all, It is possible to enroll devices into Intune when I use powershell script with same Tenant ID / App ID / App Secret, which I´m using in my C# app.

The problem shouldnt be also caused by unseficcient permissions of an app. In Azure AD, the app has these permissions, all of them with admin consent:

• DeviceManagementManagedDevices.ReadWrite.All
• DeviceManagementServiceConfig.ReadWrite.All
• DeviceManagementApps.ReadWrite.All

List of all permissions

When I was investigating communication with MS server, my app correctly calls and receives Access token from the server. But there are no packet sent after calling the register method:

graphClient.DeviceManagement.WindowsAutopilotDeviceIdentities.PostAsync(newDevice);

and It just throws exception mentioned above.

Does anybody know how to make C# app communicate with MS Intune via Graph API?

Here is a simplified example of code which I´m using:

namespace IntuneTest
{
    public partial class MainWindow : Window
    {
        private GraphServiceClient graphClient;

        public MainWindow()
        {
            InitializeComponent();
            InitializeGraphClient();
        }

        // Initialize Graph Client with ClientSecretCredential for authentication
        private async void InitializeGraphClient()
        {
            var credential = new ClientSecretCredential(
                "TenantID",   // Replace with your Tenant ID
                "AppID",      // Replace with your App ID
                "ClientSecret" // Replace with your Client Secret
            );

            graphClient = new GraphServiceClient(credential, new[] { "https://graph.microsoft.com/.default" });

            var token = await credential.GetTokenAsync(new TokenRequestContext(new[] { "https://graph.microsoft.com/.default" }), CancellationToken.None);
            Debug.WriteLine($"Access Token: {token.Token}");
        }

        // Register a Windows Autopilot device
        private async Task RegisterDeviceAsync()
        {
            try
            {
                var newDevice = new WindowsAutopilotDeviceIdentity
                {
                    SerialNumber = "6WX8WT2",   // Required: Serial number
                    Manufacturer = "Dell Inc.", // Optional
                    Model = "Latitude 5590",    // Optional
                    EnrollmentState = EnrollmentState.Enrolled
                };

                await graphClient.DeviceManagement.WindowsAutopilotDeviceIdentities.PostAsync(newDevice);
                Debug.WriteLine("Device registered.");
                MessageBox.Show("Device registered successfully!", "Success");
            }
            catch (ServiceException ex)
            {
                Debug.WriteLine($"Error: {ex.Message}");
                MessageBox.Show($"Error registering device: {ex.Message}", "Error");
            }
        }

        // Triggered by button click to register the device
        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            await RegisterDeviceAsync();
        }
    }
}

Thank you very much!