Dialogflow messenger webhook response (richcontent)

[azarug]

I've set up a Dialogflow webhook with PHP that is working fine. Receives a query and responds correctly (message shown to the user). The problem that i have is i can't figure out how to show a basic card style message (text with a link and a image) or any kind of richcontent. This only happens in Dialogflow messenger added to a webpage. This is the json i send:

{
   "source": "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaa-aaaaaaaa",
   "fulfillmentMessages": [{"card":    {
      "title": "Title",
      "subtitle": "text sample",
      "imageUri": "www.domain.com/img.png",
      "buttons": [      {
         "text": "Read",
         "postback": "www.domain.com"
      }]
   }}]
}