Unable to place order

string url = "https://api.kite.trade/orders/regular";
string postData = "api_key=xxx&access_token=yyy&tradingsymbol=ACC&exchange=NSE&transaction_type=BUY&order_type=LIMIT&quantity=2&product=CNC&price=1400&validity=DAY&trigger_price=0&tag=acc123";

byte[] data = Encoding.UTF8.GetBytes(postData);
try
{
var request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "POST";
request.ContentType = "application/json; charset=UTF-8";
request.ContentLength = data.Length;
using (var stream = request.GetRequestStream())
{
stream.Write(data, 0, data.Length);
}
var response = (HttpWebResponse)request.GetResponse();
var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();
}
catch (WebException ex)
{

}


Above code give me below eroor:
The remote server returned an error: (403) Forbidden.