Use Auth0 with Excel addin

Hello, i am building an Excel add in (local with Visual Studio in C#). In that add in i have a loginform. I am new to Auth0 and also just starting with C#. I can’t get a connection with Auth0, if I push the button in Excel on the loginform I got an error: De aanvraag is afgebroken: Kan geen beveiligd SSL/TLS-kanaal maken." (Could not establish secure channel for SSL/TLS with authority). Can please anyone help me? I use the following code:
public partial class LoginForm : Form
private AuthenticationApiClient client;
public LoginForm()

        client = new AuthenticationApiClient(
        new Uri("https://{domain}" )

    private async void btnLogin_Click(object sender, EventArgs e)
        var request = new ResourceOwnerTokenRequest
            ClientId = "{myclientid}",
            ClientSecret = "{myclientsecret}",
            Scope = "openid profile email",
            Realm = "Username-Password-Authentication", // Use the appropriate connection name
            Username = txtUsername.Text,
            Password = txtPassword.Text
            var response = await client.GetTokenAsync(request);

            if (response != null && !string.IsNullOrEmpty(response.AccessToken))
                MessageBox.Show("Login successful!");
                // Proceed with your application after successful authentication
                MessageBox.Show("Login failed.");
        //catch (Exception ex)
        //    MessageBox.Show($"Login error: {ex.Message}");

…other code.

I really appreciate if anyone can help me.

solved it by adding
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

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