If you have a SendGrid issue, please contact our support team.
When debugging or testing, it may be useful to examine the raw request body to compare against the documented format.
e.g. on a Client instance, myClient.
foreach (KeyValuePair<DateTime, string> kvp in myClient.RequestHeaders)
{
Console.WriteLine("Name = {0}, Value = {1}", kvp.Key, kvp.Value);
}