Fail to try webhook for Microsoft Teams site

anybody know if I do something wrong or if something is not working at the moment?

• I use MessageCard Playground and want to send data to a Teams-Channel.
• I did setup the connector and got a webhook url.
• Now I want to send some samples to the channel (valid json)

Getting this error:

Any idea what I do wrong?

Update

Sample JSON

{
  "@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" }
      ]
    }
  ]
}

It looks like there is a bug in MessageCard Playground at the moment which is preventing it from POSTing to the webhook endpoint properly.

I suggest trying Postman for issuing the HTTP request. You can simply copy and past the JSON from the playground. See Sending actionable messages via Office 365 Connectors for details on how to set this up.