Google API Batch Request - .NET REST Call Gives error - rest

Question

I am having .NET code to call the google api in batch request for getting the message details for multiple Ids. The request I am creating, when run through postman it works perfectly but when run this console app it gives me the Response Status code = 0 and Error Specified value has invalid CRLF characters.\r\nParameter name: value
Can someone please look into this and help me ... I have searched almost everything now but could not get any solution.
Here is my code --
var baseUrl = "/gmail/v1/users/" + _accountID + "/messages/";
RestClient client = null;
RestRequest request = null;
StringBuilder sbBody = null;
for (int j = 0; j < _messageId.Count; j++)
{
msgCount++;
if (msgCount == 1)
{
boundary = "testing_batch";
sbBody = new StringBuilder();
client = new RestClient("https://www.googleapis.com/batch/");
request = new RestRequest(Method.POST);
request.AddHeader("Content-Type", "multipart/mixed; boundary=\"" + boundary + "\"");
request.AddHeader("Authorization", "Bearer " + accessToken);
}
sbBody.Append(string.Format("--{0}\n", boundary));
sbBody.Append("Content-Type: application/http\n\n");
sbBody.Append(string.Format("GET {0}{1}\n\n", baseUrl, _messageId[j]));
if (msgCount == 1)
sbBody.Append(string.Format("--{0}--", boundary));
if (msgCount == 1)
{
msgCount = 0;
//request.AddBody(sbBody.ToString());
request.AddHeader("RequestBody", sbBody.ToString());
IRestResponse response = client.Execute(request);
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
//Do nothing for now
}
else if (response.StatusCode == System.Net.HttpStatusCode.Unauthorized)
{
Console.WriteLine(response.StatusCode);
Console.WriteLine(response.Content);
Console.ReadLine();
break;
}
else
{
Console.WriteLine(response.StatusCode);
Console.WriteLine(response.Content);
Console.ReadLine();
break;
}
}