I solved the issue, No need to add Get Streams once use Get Methods
Here are the solutions.
var httpWebRequestQR = (HttpWebRequest)WebRequest.Create(reqUrl);
httpWebRequestQR.ContentType = "application/json";
httpWebRequestQR.Method = "GET";
httpWebRequestQR.Headers.Add("Authorization", "Bearer " + accToken);
httpWebRequestQR.Headers.Add("X-Signature", signatureWc);
httpWebRequestQR.Headers.Add("X-Nonce-Str", nonce);
httpWebRequestQR.Headers.Add("X-Timestamp", timestampStr);
var httpResponseQR = (HttpWebResponse)httpWebRequestQR.GetResponse();
using (var streamReader = new StreamReader(httpResponseQR.GetResponseStream()))
{
var resultQR = streamReader.ReadToEnd();
string jsonStringsign = resultQR;
JsonData json = JsonMapper.ToObject(jsonStringsign);
string txnId = json["items"]["transactionId"].ToString();
string storeId = json["items"]["store"]["id"].ToString();
string curType = json["items"]["currencyType"].ToString();
int ttfee = (int) json["items"]["order"]["amount"];
}