Error “The remote server returned an error: (400) Bad Reques

var oAuthConsumerKey = "";

var oAuthConsumerSecret = "";

var oAuthUrl ="https://quickbooks.api.intuit.com/v3/company//invoice?minorversion=4";

// Do the Authenticate

var authHeaderFormat = "Basic {0}";

var authHeader = string.Format(authHeaderFormat,Convert.ToBase64String(Encoding.UTF8.GetBytes(Uri.EscapeDataString(oAuthConsumerKey) + ":"+Uri.EscapeDataString((oAuthConsumerSecret))) ));

string text = System.IO.File.ReadAllText("text file");

// var postBody = "grant_type=client_credentials";

HttpWebRequest authRequest = (HttpWebRequest)WebRequest.Create(oAuthUrl);

authRequest.Headers.Add("Authorization", authHeader);

authRequest.Method = "POST";

authRequest.ContentType = "application/x-www-form-urlencoded";

authRequest.UserAgent = "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 7.1; Trident/5.0)";

authRequest.Accept = "/";

authRequest.UseDefaultCredentials = true;

authRequest.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;

authRequest.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;

using (Stream stream = authRequest.GetRequestStream())

{

byte[] content = ASCIIEncoding.ASCII.GetBytes(text);

stream.Write(content, 0, content.Length);

}

authRequest.Headers.Add("Accept-Encoding", "gzip");

WebResponse authResponse = authRequest.GetResponse();