{
  "data": {
    "custom_fields": [
      {
        "id": "w1",
        "name": "pet",
        "field_type": "Text",
        "_metadata": {
          "self": "https://api.sendgrid.com/v3/marketing/field_definitions/w1"
        }
      }
    ],
    "reserved_fields": [
      {
        "id": "_rf1",
        "name": "first_name",
        "field_type": "Text",
        "_metadata": {
          "self": "https://api.sendgrid.com/v3/marketing/field_definitions/_rf1"
        }
      }
    ],
    "_metadata": {
      "count": 2,
      "self": "https://api.sendgrid.com/v3/marketing/field_definitions"
    },
    "pagination": {
      "nextPageToken": "next_page_token",
      "previousPageToken": "previous_page_token",
      "totalCount": 100
    }
  }
}