title: AWS Lex doesn't pick up user response from pressing responseCard button on facebook
body: <p>On the test bot in the AWS console, I can type out the utterances and the responses to each slot, and AWS Lex picks it up. But on Facebook Messenger, where I have set up response cards with their corresponding text and values, clicking on a button from a response card doesn't seem to reach Lex. </p>
  
  <p>I use Lambda functions to dynamically create the response cards, and it looks something like this:</p>
  
  <pre><code>{
    "dialogAction": {
      "type": "ElicitSlot",
      "intentName": "ShopIntent",
      "slots": {
          "product": null,
          "category": null
      },
      "slotToElicit": "category",
      "message": {
          "contentType": "PlainText",
          "content": "Choose a category."
      },
      "responseCard": {
          "contentType": "application/vnd.amazonaws.card.generic",
          "version": 1,
          "genericAttachments": [
              {
                  "title": "New",
                  "subTitle": "All the new things!",
                  "buttons": [{
                      "text": "New",
                      "value": "1234567890"
                   }]
              }, {
                  "title": "Shurts",
                  "subTitle": "A collection of shirts!",
                  "buttons": [{
                      "text": "Shurts",
                      "value": "1234567891"
                  }]
              }, {
                  "title": "Shuus",
                  "subTitle": "A collection of shoes!",
                  "buttons": [{
                      "text": "Shuus",
                      "value": "1234567892"
                  }]
              }
          ]
      }
    }
  }
  </code></pre>
  
  <p>This renders correctly in Facebook. But on clicking the button, nothing happens. The typing indicator appears for a few seconds (much longer than a request should take -- I wonder if this indicates some error?), then vanishes without giving any response. <em>It doesn't even create any entry in the CloudWatch log</em>. I've checked the documentation and I believe, to the best of my knowledge, that format of the <code>responseCard</code> is correct. </p>
  
  <p>I don't know how to debug this issue. Has anyone else experienced this?</p>