使用AJAX和wp_mail（）发送邮件

I am trying to build a simple ajax-powered contact form, but have no success with POST-ing to ajax-admin.php hook... I know this question has been asked a million times (I already read each one of them), so please bear with me:

Here is my Javascript:

    submitMail (e) { 
        e.preventDefault();
        const data = {
             action: 'mail_before_submit'
        };
        const ajax = new Ajax({
             method: 'POST',
             url: `${window.location.origin}/wp-admin/admin-ajax.php`,
             data: JSON.stringify(data)
        });
        ajax.on('success', (e) => {
             console.log(e)
        });
        ajax.send();
}

And here is the Wordpress hook in my functions.php:

add_action('wp_ajax_nopriv_mail_before_submit', 'mail_before_submit');
add_action('wp_ajax_mail_before_submit', 'mail_before_submit');
function mail_before_submit() {
    wp_mail('my_email_here@gmail.com', 'title text', 'body text');
    echo 'email sent';
    die();
}

I am not really sure the WP hook gets called at all. When I submit the form with JS, I can see in my console "XHR finished loading: POST "http://localhost:3000/wp-admin/admin-ajax.php".", but nothing else happens - no email is being sent and the response I get is simply a 0..

I am not that familiar with PHP, but after heavy reading I can only conclude I am doing everything right - attaching the hooks and callbacks in my functions.php file and sending a serialised JSON object with action attribute, but still without success

As you can see, it is an extremely simple example, but I have been banging my head for hours already without any success... Any help is more then appreciated!

You need to specify the action in the query parameters. Like /wp-admin/admin-ajax.php?action=mail_before_submit.

submitMail (e) { 
    e.preventDefault();
    const data = {
    };
    const ajax = new Ajax({
         method: 'POST',
         url: `${window.location.origin}/wp-admin/admin-ajax.php?action=mail_before_submit`,
         data: JSON.stringify(data)
    });
    ajax.on('success', (e) => {
         console.log(e)
    });
    ajax.send();
}