Google Chat API: How do I switch between Cards v1 and Cards v2?

According to the docs, Cards v1 is deprecated, and Cards v2 seems to be much more feature-rich.

But when I use the Cards v2 syntax, the API complains about unknown or missing fields. How can I tell the Google servers that I want to use the v2 API? The documentation does not seem to tell anything about that.

All tutorials that I can find seem to use Cards v1 only. I'm mostly following the official tutorial in Python.

Solution

I tried to send message with card v2 with this syntax:

"cards_v2": [[{
      "card_id": "addContact",
      "card": {}
}]

Request:

POST https://chat.googleapis.com/v1/spaces/space_name/messages
{
    
    "cards_v2": [{
      "card_id": "addContact",
      "card": {
        "header": {
          "title": "Rolodex",
          "subtitle": "Manage your contacts!",
          "imageUrl": "https://www.gstatic.com/images/branding/product/2x/contacts_48dp.png",
          "imageType": "CIRCLE"
        },
        "sections": [
          {
            "widgets": [
              {
                "buttonList": {
                  "buttons": [
                    {
                      "text": "Add Contact",
                      "onClick": {
                        "action": {
                          "function": "openDialog",
                          "interaction": "OPEN_DIALOG"
                        }
                      }
                    }
                  ]
                },
                "horizontalAlignment": "CENTER"
              }
            ]
          }
        ]
      }
    }]
  ,
    "thread": {
     "name": "spaces/space_name/threads/thread_name"
  }
}

Taken from here: https://developers.google.com/chat/how-tos/dialogs?hl=en