Каталог Маркетплейс

\Bitrix\Main\EventManager::getInstance()->addEventHandler(
    'slytek.maxnotify',
    'onMessageGet',
    ['MaxnotifyHandler', 'onMessageGet']
);
\Bitrix\Main\EventManager::getInstance()->addEventHandler(
    'slytek.maxnotify',
    'onButtonsGet',
    ['MaxnotifyHandler', 'onButtonsGet']
);

class MaxnotifyHandler
{
    public static function onMessageGet(\Bitrix\Main\Event $event)
    {
        $message = $event->getParameter('message');
        $chat_id = $event->getParameter('chat_id');
        $buttons = $event->getParameter('buttons');
        $user_name = $event->getParameter('user_name');
        $first_name = $event->getParameter('first_name');
        $last_name = $event->getParameter('last_name');

        $res = [];

        if ($message == 'test')
        {
            $buttons[] = 'test';
            $buttons[] = 'test2';
            $res = [
                'buttons' => $buttons,
                'message' => $first_name . ' ' . $last_name . ' [' . $user_name . '] said ' . $message,
            ];
        }

        $result = new \Bitrix\Main\EventResult(\Bitrix\Main\EventResult::SUCCESS, $res);

        return $result;
    }

    public static function onButtonsGet(\Bitrix\Main\Event $event)
    {
        $buttons = $event->getParameter('buttons');
        $params = $event->getParameter('params');
        if ($params['message'] == 'test2')
        {
            $buttons[] = $params['user_name'];
        }
        $result = new \Bitrix\Main\EventResult(\Bitrix\Main\EventResult::SUCCESS, $buttons);

        return $result;
    }
}

\Bitrix\Main\Loader::includeModule('slytek.maxnotify');
echo 'https://max.ru/КОД_БОТА?start='.\Slytek\Max\Notify::authLink();

https://max.ru/КОД_БОТА?start=ID_ЗАКАЗА-ТЕЛЕФОН_ИЛИ_EMAIL 
или вида 
https://max.ru/КОД_БОТА?start=base64_encode('ID_ЗАКАЗА|ТЕЛЕФОН_ИЛИ_EMAIL')