curl --request POST \
  --url https://api.klavis.ai/sandbox/resend/{sandbox_id}/initialize \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "emails": [
    {
      "from": "<string>",
      "to": [
        "<string>"
      ],
      "subject": "<string>",
      "id": "<string>",
      "html": "<string>",
      "text": "<string>",
      "reply_to": "<string>",
      "cc": [
        "<string>"
      ],
      "bcc": [
        "<string>"
      ],
      "tags": [
        {}
      ],
      "created_at": "<string>"
    }
  ],
  "contacts": [
    {
      "email": "<string>",
      "id": "<string>",
      "first_name": "<string>",
      "last_name": "<string>",
      "unsubscribed": false,
      "created_at": "<string>"
    }
  ],
  "segments": [
    {
      "name": "<string>",
      "id": "<string>",
      "created_at": "<string>",
      "broadcasts": [
        {
          "from": "<string>",
          "subject": "<string>",
          "id": "<string>",
          "name": "<string>",
          "html": "<string>",
          "text": "<string>",
          "reply_to": "<string>",
          "status": "<string>",
          "created_at": "<string>",
          "scheduled_at": "<string>",
          "sent_at": "<string>",
          "topic_id": "<string>"
        }
      ]
    }
  ]
}
'

{
  "sandbox_id": "<string>",
  "status": "idle",
  "message": "<string>",
  "records_created": {}
}