title: C# HttpClient, getting error Cannot add value because header 'content-type' does not support multiple values
body: <pre><code>HttpClient serviceClient = new HttpClient();
  serviceClient.DefaultRequestHeaders.Add("accept", "Application/JSON");
  
  HttpContent content = new StringContent(text);
  content.Headers.Add("content-type", "text/html");
  
  var response = await serviceClient.PostAsync(new Uri(_serviceUrl), content);
  </code></pre>
  
  <p>This is my code. I want to do a POST, and set the content type to text/html, but when I do this I get the above error.</p>
  
  <p>I can set the content type it seems via <code>content.Headers.ContentType</code> but I don't know how to specifcy "text/html" if I do that. Can anyone help?</p>