pivi_vault_system/api/province/index.php

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

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