جواب رو پیدا کردم:
var httpWebRequest = (HttpWebRequest)WebRequest.Create("http://plusserver.pluschap.com/plusservice/plustime/createplustime");
httpWebRequest.ContentType = "application/json";
httpWebRequest.Method = "POST";
int year = Convert.ToInt32(txtPlusTimeYear.Text.Trim());
int month = Convert.ToInt32(txtPlusTimeMonth.Text.Trim());
int day = Convert.ToInt32(txtPlusTimeDay.Text.Trim());
DateTime georgianDateTime = new DateTime(year, month, day, new System.Globalization.PersianCalendar());
//var dte = DateTime.ParseExact(georgianDateTime.ToShortDateSt ring(), "Mmm dd, yyyy ", CultureInfo.InvariantCulture);
string dte = georgianDateTime.ToString("MMM dd, yyyy ");
String date = dte + txtPlusTimeHour.Text.Trim() + ":" + txtPlusTimeMinute.Text.Trim() + ":" + txtPlusTimeSecond.Text.Trim();
//pattern: Apr 25, 2019 05:37:25
using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
{
string json = "{"enable":"true","title":"" + date + "","registerdate":"2020-10-10","establishtime":"2020-10-10"}";
streamWriter.Write(json);
streamWriter.Flush();
streamWriter.Close();
}
var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
{
var result = streamReader.ReadToEnd();
}