DoliTicketing/custom/documentfollower/ajax/levels.php

<?php
require '../../../main.inc.php';
require_once DOL_DOCUMENT_ROOT.'/user/class/user.class.php';
require_once DOL_DOCUMENT_ROOT.'/user/class/usergroup.class.php';

//$filter = GETPOST('filter', 'alpha');
$action = GETPOST('action', 'aZ09');
//$id = GETPOST('id', 'int');

if ($action == 'list') {
    $result = [
        'users' => [],
        'groups' => []
    ];

    // load users
    

    // load user groups
    

    echo json_encode($result);  
}


//echo json_encode($outjson);