I found the reason is that you send owner as a string. You need to send the owner as an object containing the id of the related user.

POST /api/batches
{
  "data": {
    "name": "Test Batch",
    "state": "open",
    "locale": "vi",
    "owner": {
      "id": "rz9blkq8c0bns6bxx81heq9w"
    }
  }
}