How to show current garage door state on Google Home?

I have implemented a google actions backend that successfully communicates with Google Home/Assistant to open/close my garage door.

The SYNC replies with one device:

{
  "requestId": "XXX",
  "payload": {
    "agentUserId": "XXX",
    "devices": [
      {
        "id": "XXXX",
        "type": "action.devices.types.GARAGE",
        "traits": [
          "action.devices.traits.OpenClose"
        ],
        "name": {
          "name": "Garage XXXX"
        },
        "willReportState": false,
        "roomHint": "garage",
        "attributes": {
          "discreteOnlyOpenClose": true,
          "commandOnlyOpenClose": false,
          "openDirection": [
            "UP",
            "DOWN"
          ]
        },
        "deviceInfo": {
          "manufacturer": "XXX"
        }
      }
    ]
  }
}

When I open the app, I receive a QUERY:

{
  "inputs": [
    {
      "intent": "action.devices.QUERY",
      "payload": {
        "devices": [
          {
            "id": "XXX"
          }
        ]
      }
    }
  ],
  "requestId": "XXX"
}

to which I reply:

{
  "requestId": "XXX",
  "payload": {
    "agentUserId": "XXX",
    "devices": {
      "XXX": {
        "online": true,
        "status": "SUCCESS",
        "openPercent": 0
      }
    }
  }
}

I think I did right by answering that my device is a garage door, and I report that it's currently closed. However the app does not show a button to trigger an open/close action.

How can I have the app show a button like a light switch? Currently when I click on the device in the app, it just displays information (like the vendor, device name, etc) but no button and no actionable thing.

It does work though when I speak "open the garage", and the garage door opens successfully when I process the EXECUTE.

Not all device types and traits support the UI control at the moment. You can find the list of supported device types and traits on the google smart home documentation: developers.google.com/assistant/smarthome/develop/… .

I would also recommend opening up a feature request on the public issue tracker in this regard so that we can place it on our future development roadmap for feature enhancements.