title: Can't get Topics endpoint in Cognitive Services
body: <p>I was trying to run a sample app that gets the topics endpoint for microsoft cognitive services Text Analytics API but the function return 400 HTTP error.</p>
  
  <p>Here is the code:</p>
  
  <pre><code>static async Task&lt;string&gt; CallTopicEndpoint(HttpClient client, string uri, byte[] byteData)
  {
      using (var content = new ByteArrayContent(byteData))
      {
          content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
          var response = await client.PostAsync(uri, content);
          // Return URL containing OperationID to poll from.
          return response.Headers.GetValues("Operation-Location").First();
      }
  }
  </code></pre>
  
  <p>Full sample is in here:
  <a href="https://text-analytics-demo.azurewebsites.net/Home/SampleCode" rel="nofollow noreferrer">https://text-analytics-demo.azurewebsites.net/Home/SampleCode</a></p>
  
  <p>Any help is appreciate it.</p>
  
  <p>Thanks.</p>