add_action('wp_ajax_send_training_order', 'send_training_order');
add_action('wp_ajax_nopriv_send_training_order', 'send_training_order');

function send_training_order() {

    $places     = sanitize_text_field($_POST['places']);
    $name_title = sanitize_text_field($_POST['name_title']);
    $company    = sanitize_text_field($_POST['company']);
    $email      = sanitize_email($_POST['email']);
    $telephone  = sanitize_text_field($_POST['telephone']);

    $to      = "you@plustraining.co.uk"; // change to your email
    $subject = "New Training Order Enquiry";

    $message = "
A new training order enquiry has been submitted:

Number of places: $places
Name & Job Title: $name_title
Company: $company
Email: $email
Telephone: $telephone
";

    wp_mail($to, $subject, $message, [
        'From: website@plustraining.co.uk',
        'Reply-To: ' . $email
    ]);

    echo "Thank you — your enquiry has been sent. We will contact you shortly.";
    wp_die();
}
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="https://health-and-safety-lancashire.co.uk/wp-sitemap-index.xsl" ?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"><sitemap><loc>https://health-and-safety-lancashire.co.uk/wp-sitemap-posts-post-1.xml</loc></sitemap><sitemap><loc>https://health-and-safety-lancashire.co.uk/wp-sitemap-posts-page-1.xml</loc></sitemap><sitemap><loc>https://health-and-safety-lancashire.co.uk/wp-sitemap-taxonomies-category-1.xml</loc></sitemap><sitemap><loc>https://health-and-safety-lancashire.co.uk/wp-sitemap-taxonomies-post_tag-1.xml</loc></sitemap><sitemap><loc>https://health-and-safety-lancashire.co.uk/wp-sitemap-users-1.xml</loc></sitemap></sitemapindex>