message_two_charts.json

{
  "channel": "C123",
  "text": "",
  "mrkdwn": true,
  "blocks": [
    {
      "type": "data_visualization",
      "block_id": "chart_0",
      "title": "Chart",
      "chart": {
        "type": "pie",
        "segments": [
          {
            "label": "A",
            "value": 1
          }
        ]
      }
    },
    {
      "type": "data_visualization",
      "block_id": "chart_1",
      "title": "Chart",
      "chart": {
        "type": "pie",
        "segments": [
          {
            "label": "A",
            "value": 1
          }
        ]
      }
    }
  ]
}