title: 500 when trying to send message to bot via Direct Line API
body: <p>I'm building a client which will interact with an existing bot built using the Microsoft Bot Framework. The bot works fine when I test with the existing channels. I can also successfully start a conversation when using the Direct Line API. However when I try to send a message to the bot using Direct Line API I get a 500 error with content "ServiceError".</p>
  
  <p>I am sending an http Post request using Fiddler to <a href="https://directline.botframework.com/v3/directline/conversations/[MyConversationID]/activities" rel="nofollow noreferrer">https://directline.botframework.com/v3/directline/conversations/[MyConversationID]/activities</a> with the following header:</p>
  
  <pre><code>Authorization: Bearer &lt;My Secret&gt; 
  Host: directline.botframework.com
  Content-Length: 97
  </code></pre>
  
  <p>And Body</p>
  
  <pre><code>{
      "type": "message",
      "from": {
          "id": "user1"
      },
      "text": "hello"
  }
  </code></pre>
  
  <p>I am fairly certain the issue is not in my bot code as no breakpoint is hit. Has anyone had a similar issue? Or have any advice on how to go about debugging it?</p>