pivi_vault_system/api/city/index.php

<?php
include_once '../../editor/lib/DataTables.php';

$city = $db
    ->select( 'city', ['id as value', 'name as label'], ['pid' => $_REQUEST['values']['documents.province']] )
    ->fetchAll();
 
echo json_encode( [
    'options' => [
        'documents.city' => $city
    ]
] );