title: Fail to try webhook for Microsoft Teams site
body: <p>anybody know if I do something wrong or if something is not working at the moment?</p>
  
  <ul>
  <li>I use <a href="https://messagecardplayground.azurewebsites.net/" rel="nofollow noreferrer">MessageCard Playground</a> and want to send data to a Teams-Channel.</li>
  <li>I did setup the connector and got a webhook url.
  <a href="https://i.stack.imgur.com/fyphG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fyphG.png" alt="enter image description here"></a></li>
  <li>Now I want to send some samples to the channel (valid json)</li>
  </ul>
  
  <p>Getting this error:
  <a href="https://i.stack.imgur.com/nuyRI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nuyRI.png" alt="enter image description here"></a></p>
  
  <p>Any idea what I do wrong?</p>
  
  <p><strong>Update</strong></p>
  
  <p>Sample JSON</p>
  
  <pre><code>{
    "@type": "MessageCard",
    "@context": "http://schema.org/extensions",
    "summary": "Issue 4711",
    "themeColor": "0078D7",
    "title": "Issue opened: \"TEST Message for webhook\"",
    "sections": [
      {
        "activityTitle": "Yves Rausch",
        "activitySubtitle": "10/12/2017, 22:34",
        "facts": [
          {
            "name": "Title:",
            "value": "TinyMCE 4 implementieren"
          },
          {
            "name": "Issue #:",
            "value": "6417"
          }
        ],
        "text": "There is a push webhook info and leads me to the workflow."
      }
    ],
    "potentialAction": [
      {
        "@type": "OpenUri",
        "name": "View in process",
        "targets": [
          { "os": "default", "uri": "https://intranet.tqsoft.net/ror/workflowact/6417" }
        ]
      }
    ]
  }
  </code></pre>