ajax_hit.php

См. документацию.

<?php
 
if (
    isset($_SERVER["REQUEST_METHOD"], $_REQUEST["IM_AJAX_CALL"])
    && $_SERVER["REQUEST_METHOD"] === "POST"
    && $_REQUEST["IM_AJAX_CALL"] === "Y"
)
{
    $arResult = [];
    global $USER, $APPLICATION, $DB;
    include($_SERVER["DOCUMENT_ROOT"]."/bitrix/components/bitrix/im.messenger/im.ajax.php");
    die();
}
?>