curl --request POST \
  --url 'https://api.flashcat.cloud/calendar/event/list?app_key=' \
  --header 'Content-Type: application/json' \
  --data '
{
  "cal_id": "<string>",
  "year": 123,
  "month": 123,
  "day": 123
}
'

{
  "error": {
    "code": "<string>",
    "message": "<string>"
  },
  "data": {
    "items": [
      {
        "cal_id": "<string>",
        "summary": "<string>",
        "creator_id": 123,
        "is_off": true,
        "start_at": "<string>",
        "end_at": "<string>",
        "created_at": 123,
        "updated_at": 123,
        "event_id": "<string>",
        "description": "<string>"
      }
    ],
    "total": 123
  }
}