How to send a 404 error source to a VK message via api?

Question

API

There is an interesting idea that is now working, but it does not work completely smoothly. All this is implemented on wp with a custom 404 page. The code that below clings to the 404 page and sends a message to VK (the site runs a script that crashes from time to time (+ the plugin overwrites an important file and everything breaks (cancel the recording is not a variant), but operational there is no way - how to find out in time that the errors have gone)
// I immediately say in the code I don’t rummage at all - a dense forest)
Code

function wpd_do_stuff_on_404(){
    if( is_404() ){
           $url = 'https://api.vk.com/method/messages.send';
    $params = array(
        'user_id' => $id = '266212779',    // Кому отправляем, если взять вместо и вставить user_ids тогда можно будет добавлять id через запятую (сообщение будет отправляться 2х пользователям)
        'message' => $message = '<br>__ ▂ ▃ ▅ ▇ █ ｡◕‿ ◕｡ █ ▇ ▅ ▃ ▂ __<br>Привет! На сайте появилась ошибка 404<br>Проверь пожалуйста<br>[ ▇ ▃ ▄ ▅ █ ▇ ▂ ▃ ▁ ▄ ▅ █ ▅ ▃ ▇ ]',   // Что отправляем
        'access_token' => '0000000000000000000000000',  // access_token можно вбить хардкодом, если работа будет идти из под одного юзера
        'v' => '5.37',
    );

    // В $result вернется id отправленного сообщения
    $result = file_get_contents($url, false, stream_context_create(array(
        'http' => array(
            'method'  => 'POST',
            'header'  => 'Content-type: application/x-www-form-urlencoded',
            'content' => http_build_query($params)
        )
    )));
    }
}
add_action( 'template_redirect', 'wpd_do_stuff_on_404' );

Actually the question is how to pass a link to the source of the 404 ps error in the message field in the wp engine
so that the code works in the 404.php file this was added -

<?php echo do_shortcode( '  [wbcr_php_snippet id="1135"]' ); ?> (плагин добаления шорткодов, потому что как вывести в странице код ошибки я не знаю, а вот как добавить шорткод в php это я нагуглил)
<?php echo do_action('template_redirect'); ?>

the code was taken from some article on habré
, a hook was found to hook the 404 page (thanks to the chela from the toaster (habr questions)

Answer 1

display the error code in the page I do not know

But find out. And do not fence such crutches with shortcodes.

<?php echo do_action('template_redirect'); ?>

This is completely off topic since the VI executes the template_redirect hook itself.
And the answer to your question is googled in 10 seconds:
https://stackoverflow.com/a/6768831
Get the requested URL and add it to the message text

Answer 2

But <?php echo do_action('template_redirect'); ?>it was inserted there not by experience ... Namely, a code was taken that captures the 404 page (I had a question in my profile, like how to capture 404)
+ What will be the code that would make it all work?
What do you need to write to send?
Minimum code knowledge