Unauthorized Error While Accesing Filpkart Marketplace API

using (HttpClient httpClient = new HttpClient())

{

HttpContent content = new FormUrlEncodedContent(new[]

{

new KeyValuePair("appid:app-secret", "appID:appSecret"),

});

content.Headers.Clear();

content.Headers.Add("Content-Type", "application/octet-stream");

HttpResponseMessage response = httpClient.PostAsync("https://api.flipkart.net/oauth-service/oauth/token?grant_type=client_credentials&scope=Seller_Api", content).Result;

}