curl --request GET \
  --url https://api.sanka.com/v1/public/calendar/availability

{
  "message": "<string>",
  "days": [
    {
      "date": "<string>",
      "day_index": 123,
      "weekday": "<string>",
      "slots": [
        "<string>"
      ]
    }
  ],
  "timezone": "<string>",
  "ctx_id": "<string>"
}