List Custom Fields

{
  "items": [
    {
      "id": "string",
      "entity_type": "user",
      "key": "string",
      "label": "string",
      "description": "string",
      "field_type": "text",
      "is_required": true,
      "is_user_editable": true,
      "is_user_visible": true,
      "options": [
        null
      ],
      "is_active": true,
      "created_at": null,
      "updated_at": null
    }
  ],
  "total": 0,
  "page": 1,
  "size": 1,
  "pages": 0
}

{
  "detail": [
    {
      "loc": [
        "string"
      ],
      "msg": "string",
      "type": "string",
      "input": null,
      "ctx": {}
    }
  ]
}