korshunov_pro

\Bitrix\Main\EventManager::getInstance()->addEventHandler(
    'main',
    'OnBeforeLocalRedirect',
    'formBeforeRedirect'
);

function formBeforeRedirect($redirectUrl) {
    parse_str(parse_url($redirectUrl, PHP_URL_QUERY), $query);
    if (!empty($query['WEB_FORM_ID']) && !empty($query['formresult'])) {
        die(json_encode([
            'error' => 0,
            'message' => ''
        ]));
    }
}