Block structure in Flex Message

flex-block.json

{
  "type": "bubble",
  "header": {
    "type": "box",
    "layout": "vertical",
    "contents": [
      {
        "type": "text",
        "text": "header"
      }
    ]
  },
  "hero": {
    "type": "image",
    "url": "https://www.linefriends.com/img/img_sec.jpg",
    "size": "full",
    "aspectRatio": "2:1"
  },
  "body": {
    "type": "box",
    "layout": "vertical",
    "contents": [
      {
        "type": "text",
        "text": "body"
      },
	  {
        "type": "text",
        "text": "body"
      }
    ]
  },
  "footer": {
    "type": "box",
    "layout": "vertical",
    "contents": [
      {
        "type": "text",
        "text": "footer"
      }
    ]
  }
}