I tried different methods non of them are working. I don't know where is the problem. so far I tried these lines. 1st
client.DefaultRequestHeaders.Add("Connection", "Keep-Alive");
2nd
HttpContent postdata = postdata2;
postdata.add("Keep-Alive","true");
If I write client.DefaultRequestHeaders.Add("Connection", "Close"); it shows in fiddler header. However Keep-Alive is not working. I seen similar questions on here. But non of the questions got the answer.