var userSession = new UserSessionData
{
    User = "Facebook Email or Phone number",
    Password = "Facebook Password"
};

IFacebookApi FacebookApi = FacebookApiBuilder.CreateBuilder()
    .SetUser(userSession)
    //.UseLogger(new FileDebugLogger(LogLevel.All))
    .UseLogger(new DebugLogger(LogLevel.All))
    .SetRequestDelay(RequestDelay.FromSeconds(0, 1))
    // Session handler, set a file path to save/load your state/session data
    .SetSessionHandler(new FileSessionHandler { FilePath = StateFile })

    //// Setting up proxy if you needed
    //.UseHttpClientHandler(httpClientHandler)
    .Build();

FacebookApi.SimCountry = FacebookApi.NetworkCountry = "us"; // lower case < us => united states
FacebookApi.ClientCountryCode = "US"; // most be upper case <US =>  united states
FacebookApi.AppLocale = FacebookApi.DeviceLocale = "en_US"; // if you want en_US , no need to set these


// load old session
FacebookApi.SessionHandler?.Load();

if (!FacebookApi.IsUserAuthenticated) // if we weren't logged in
{
    await FacebookApi.SendLoginFlowsAsync();

    var loginResult = await FacebookApi.LoginAsync();
    if (loginResult.Succeeded)// logged in
    {
        //// library will saves session automatically, so no need to do this:
        //FacebookApi.SessionHandler?.Save();
        Connected();
        // after we logged in, we need to sends some requests
        await FacebookApi.SendAfterLoginFlowsAsync();
    }
    else
    {
        switch (loginResult.Value)
        {
            case FacebookLoginResult.WrongUserOrPassword:
                MessageBox.Show("Wrong Credentials (user or password is wrong)");

                break;

            case FacebookLoginResult.RenewPwdEncKeyPkg:
                MessageBox.Show("Press login button again");
                break;
        }
    }
}
else
{
    Connected();
}