Connecting Xamarin with web api

Question

My Webapi Code

 

[HttpGet]
public HttpResponseMessage SendMail1(string tomail)
{
    bool responce = false;
    try
    {
        MailMessage mail = new MailMessage();
        SmtpClient smtpServer = new SmtpClient();
        string password = ConfigurationManager.AppSettings["password"];
        mail.From = new MailAddress(ConfigurationManager.AppSettings["MailFrom"]);
        //string[] toRecipients = vm.ToRecipients.Split(',');
        //foreach (string toRecipient in toRecipients)
        //{
        //    if (!string.IsNullOrEmpty(toRecipient))
        //        mail.To.Add(new MailAddress(toRecipient));
        //}
        mail.To.Add(new MailAddress(tomail));
        mail.Subject = "subject";
        mail.Body = "body txt";
        //vm.FromRecipients = ConfigurationManager.AppSettings["MailFrom"];
        smtpServer.Host = ConfigurationManager.AppSettings["Host"];
        smtpServer.Port = int.Parse(ConfigurationManager.AppSettings["Port"]);
        smtpServer.DeliveryMethod = SmtpDeliveryMethod.Network;
        smtpServer.EnableSsl = bool.Parse(ConfigurationManager.AppSettings["EnableSsl"]);
        smtpServer.Timeout = 100000;
        smtpServer.Credentials = new System.Net.NetworkCredential(ConfigurationManager.AppSettings["MailFrom"], password);
        smtpServer.Send(mail);

        var Result = this.Request.CreateResponse(HttpStatusCode.OK, responce, new JsonMediaTypeFormatter());

        return Result;
    }
    catch (Exception ex)
    {
        HttpError Error = new HttpError(ex.Message) { { "IsSuccess", false } };
        return this.Request.CreateErrorResponse(HttpStatusCode.OK, Error);
    }

}

This is my Xamarin Code

 

private async void btnLogin_Clicked(object sender, EventArgs e)

   try
   {
       EmailConfigDetailsVM emildetails = new EmailConfigDetailsVM();
       HttpClient client = new HttpClient();
       string apiUrl = "http://localhost:52869/api/default/sendmail1?tomail=";
       emildetails.ToRecipients ="*********@gmail.com";
       emildetails.Body ="test";
       emildetails.Subject = "test";
       var serializedProduct = JsonConvert.SerializeObject(emildetails);
       var content = new StringContent(serializedProduct, Encoding.UTF8, "application/json");
       HttpResponseMessage response = client.GetAsync(apiUrl+ "*********@gmail.com").Result;
       if (response.IsSuccessStatusCode)
       {
           DisplayAlert("Alert", "Send Successfully", "OK");
       }
       else
       {
           DisplayAlert("Alert", "Send Failed...", "OK");
       }
   }
   catch (Exception ex)
   {
       string err = ex.InnerException.ToString();
       errormsg.Text = ex.Message.ToString();
   }

 it throw an exception in xamrin: Exception has been thrown by the target of an invocation.

 

Please help me.