Connecting Xamarin with web api

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.