PostAsync is not working properly, whenever executed it gives exception in the catch.

Hi guys,
I'm having problem executing "PostAsync" as it is giving unusual error, My whole code works fine except the line with "PostAsync". The weird thing is that , it posts the content to the database through PostAsync successfully but then jumps to "Catch" and throws exception. I have given my code below, what am I doing wrong..?

FYI: I'm using Xamarin.Forms and the database is Sharepoint list

try
{
using (var client = new HttpClient()
{ Timeout = TimeSpan.FromSeconds(5) })
using (var content = new MultipartFormDataContent())
{
var values = new[]
{
new KeyValuePair<string, string>("PinCode", pincode),
new KeyValuePair<string, string>("Email", email),
new KeyValuePair<string, string>("FirstName", firstname),
new KeyValuePair<string, string>("MiddleName", middlename),
new KeyValuePair<string, string>("FamilyName", familyname)

                       };

                    foreach (var keyValuePair in values)
                        content.Add(new StringContent(keyValuePair.Value), keyValuePair.Key);

                   using (var result = await client.PostAsync(requestUri, content).ConfigureAwait(false))  //App Jumps to Catch and don't execute further
                       {
                            var input = await result.Content.ReadAsStringAsync().ConfigureAwait(false);

                            if (result.IsSuccessStatusCode)
                            {
                                await DisplayAlert("Response:>", result.StatusCode.ToString(), "OK");
                                submit.IsEnabled = false;
                            }
                            else await DisplayAlert("Response:>", "Unsuccessful", "OK");
                       }
                }
        }
        catch (TaskCanceledException ex)
        {
            if (ex.CancellationToken.IsCancellationRequested == false)
            {  await DisplayAlert("ex", "Unsuccessful", "OK");   }
            else
            { await DisplayAlert("ex", "true~~~~", "OK");  }

}