Error when trying to authentifcate against Azure AD

I am using a MSAL WinForms example

    WindowsBrokerOptions brokerOptions = new WindowsBrokerOptions(); // (WindowsBrokerOptions.OperatingSystems.Windows);

string Instance = "https://login.microsoftonline.com/";
    

    _clientApp = PublicClientApplicationBuilder.Create(_clientId)
        .WithAuthority($"{Instance}{_tenantId}")
        .WithDefaultRedirectUri()
        .WithWindowsBrokerOptions(brokerOptions)
        .Build();

    MsalCacheHelper cacheHelper = CreateCacheHelperAsync().GetAwaiter().GetResult();

    // Let the cache helper handle MSAL's cache, otherwise the user will be prompted to sign-in every time.
    cacheHelper.RegisterCache(_clientApp.UserTokenCache);

    AuthenticationResult authResult = null;
    //var app = App.PublicClientApp;
    GraphResultsTextBox.Text = string.Empty;
    AccessTokenSourceLabel.Text = string.Empty;

    // if the user signed-in before, remember the account info from the cache
    IAccount firstAccount = (await _clientApp.GetAccountsAsync()).FirstOrDefault();

    // otherwise, try witht the Windows account
    if (firstAccount == null)
    {
        firstAccount = PublicClientApplication.OperatingSystemAccount;
    }

    try
    {
        authResult = await _clientApp.AcquireTokenSilent(scopes, firstAccount)
            .ExecuteAsync();
    }
    catch (MsalUiRequiredException ex)
    {
        // A MsalUiRequiredException happened on AcquireTokenSilent. 
        // This indicates you need to call AcquireTokenInteractive to acquire a token
        System.Diagnostics.Debug.WriteLine($"MsalUiRequiredException: {ex.Message}");

        try
        {
            authResult = await _clientApp.AcquireTokenInteractive(scopes)
                .WithAccount(firstAccount)
                //.WithParentActivityOrWindow( // optional, used to center the browser on the window
                .WithPrompt(Prompt.SelectAccount)
                .ExecuteAsync();
        }
        catch (MsalException msalex)
        {
            GraphResultsTextBox.Text = $"Error Acquiring Token:{System.Environment.NewLine}{msalex}";
        }
    }
    catch (Exception ex)
    {
        GraphResultsTextBox.Text = $"Error Acquiring Token Silently:{System.Environment.NewLine}{ex}";
        return;
    }

    if (authResult != null)
    {
        GraphResultsTextBox.Text = await GetHttpContentWithToken(graphAPIEndpoint, authResult.AccessToken);
        GraphResultsTextBox.Visible = true;
        DisplayBasicTokenInfo(authResult);
        this.SignOutButton.Visible = true;
        
    }

    SignInCallToActionLabel.Hide();
    GraphResultsPanel.Show();

When I run it a browser opens and I select the correct account.

I then get the following in the browser

Authentication complete. You can return to the application. Feel free to close this browser tab.

However authResult is null and I get the following

rror Acquiring Token: MSAL.NetCore.4.70.0.0.MsalServiceException: ErrorCode: invalid_client Microsoft.Identity.Client.MsalServiceException: A configuration issue is preventing authentication - check the error message from the server for details. You can modify the configuration in the application registration portal. See https://aka.ms/msal-net-invalid-client for details. Original exception: AADSTS7000218: The request body must contain the following parameter: 'client_assertion' or 'client_secret'.

I tried enabling public flow as per numerous Google results - but that did not work.

Interestingly it works on my Azure AD but when I try on a production AD for another tenant it does not - yes the ID's are call correct :)

Any ideas?

Here are my redirect config plus a http://localhost

The error "AADSTS7000218: The request body must contain the following parameter: 'client_assertion' or 'client_secret'" usually occurs if the Microsoft Entra ID application is not enabled as Public.

Make sure to set Allow public client flows to "Yes":

And also make sure to configure the redirect URL under Mobile and desktop applications platform:

Also make sure that you have no other platforms which is configured with redirect URL like below:

Delete Web redirect URLs:

If it's configured, then delete other platforms and keep only Mobile and desktop applications platform to resolve the issue.