How to echo referral post custom field (ACF) value with help of Referer HTTP in wordpress?

Question

Advance custum field Ultrasurf Portable

When i click download button on https://pkhorse.com/ it goes to i need to echo refferal post custum field value into second page.. Thiscode is working for title https://pkhorse.com/inpage-urdu-2009/

 `<?php
    $url = htmlspecialchars($_SERVER['HTTP_REFERER']);
    $back_id = url_to_postid($_SERVER['HTTP_REFERER']);
    if( $back_id > 0 ){
         $back_title = get_the_title( $back_id );
         echo "<a href='{$url}'>Go back to the {$back_title}</a>"; 
    }
?>
I want something from referral page 
<?php the_field('url'); ?> `