How to enable Display Interface?

I am working on Alexa Voice Service using a Device with Alexa build-in. I am having problems getting "Display.RenderTemplate" directives working on my device. Found documentation here:

https://developer.amazon.com/docs/custom-skills/display-interface-reference.html

https://developer.amazon.com/docs/custom-skills/display-template-reference.html

This is an example of the response of my skill:

{
  "version": "1.0",
  "response": {
    "outputSpeech": {
      "type": "SSML",
      "ssml": "<speak>Welcome back to U.S. University Finder. <break time=\"500ms\"/>It looks like you're not done filling out your profile. Do you want to finish it now?</speak>"
    },
    "reprompt": {
      "outputSpeech": {
        "type": "SSML",
        "ssml": "<speak>Welcome back to U.S. University Finder. <break time=\"500ms\"/>It looks like you're not done filling out your profile. Do you want to finish it now?</speak>"
      }
    },
    "shouldEndSession": false,
    "directives": [
      {
        "type": "Display.RenderTemplate",
        "template": {
          "type": "BodyTemplate6",
          "token": "Main",
          "backButton": "HIDDEN",
          "backgroundImage": {
            "sources": [
              {
                "url": "https://unsplash.com/photos/2RouMSg9Rnw"
              }
            ]
          },
          "textContent": {
            "primaryText": {
              "text": "U.S. University Finder",
              "type": "PlainText"
            }
          }
        }
      },
      {
        "type": "Hint",
        "hint": {
          "type": "PlainText",
          "text": "search for schools in Washington"
        }
      }
    ]
  },
  "userAgent": "ask-node/2.7.0 Node/v8.11.1",
  "sessionAttributes": {
    "PREVIOUS_INTRO_MESSAGE": "Searching for Biological and Biomedical Sciences.",
    "MAJOR": "Biological and Biomedical Sciences",
    "FIRST_RUN": false,
    "INTRO_MESSAGE": "Welcome back to U.S. University Finder. <break time=\"500ms\"/>It looks like you're not done filling out your profile. Do you want to finish it now?",
    "isInitialized": true,
    "SKILL_STATE": "_PROFILE_MODE"
  }
}

When the skill sends that response, AVS returns an error saying the device can not handle the directive.

At first, I thought enabling the "TemplateRuntime 1.0" interface will fix the problem. But that interface only enables cards for skill responses' like this:

{
  "version": "1.0",
  "response": {
    "outputSpeech": {"type":"PlainText","text":"Your Ride Hailer car is on the way!"},
    "card": {
      "type": "Standard",
      "title": "Ordering a Car",
      "text": "Your ride is on the way to 123 Main Street!\nEstimated cost for this ride: $25",
      "image": {
        "smallImageUrl": "https://ridehailer.com/resources/card-images/race-car-small.png",
        "largeImageUrl": "https://ridehailer.com/resources/card-images/race-car-large.png"
      }
    }
  }
}

I couldn't find any capability to enable "Display.RenderTemplate" and "Hint" directives in the documentation.

Do you know how to get those directives working on my device?

Thanks in advance.