How to correctly determine the site id when sending a CEvent::Send message?

Question

1C-Bitrix

Kind.

Multisite is done on folders. Everything is specified in the settings of the second site. The mail template is attached to the second site. The code below is a handler and is located in a separate folder in the template of the second site. When submitting the form, the site id is incorrectly determined. In public, I checked what is displayed by the SITE_ID constant - everything is OK "s2". If you attach the mail template to s1, then everything works. How to specify id correctly? why Error?

<?
define("NO_KEEP_STATISTIC", true);
require($_SERVER["DOCUMENT_ROOT"]."/bitrix/modules/main/include/prolog_before.php");


if (isset($_POST) && count($_POST) > 0) {
    switch($_POST['a']) {
        
    case 'callback':
      $mess = '';
            if (strlen(trim($_POST['name'])) == 0) {
                $mess .= '<p><font class="errortext">Укажите ваше имя.</font></p>';
            }
            if (strlen(trim($_POST['phone'])) < 10) {
                $mess .= '<p><font class="errortext">Укажите номер телефона в федеральном формате.</font></p>';
            }
            if ($mess == '') {

                CEvent::Send("CALLBACK", SITE_ID, array(
                    "SERVICE" => trim($_POST['service']),
                    "NAME" => trim($_POST['name']),
                    "PHONE" => trim($_POST['phone'])
                ), "N");
        $mess = '<div class="mf-ok-text"><b>Спасибо, ваше сообщение принято.</b></div>';
            }
      echo $mess;//.'|'.$code;
            break;
    }
}

require($_SERVER["DOCUMENT_ROOT"]."/bitrix/modules/main/include/epilog_after.php");
?>

Answer 1

and if so \Bitrix\Main\Application::getInstance()->getContext()->getSite() ??