{WP} AJAX call from URL

wp_ajax_url_call.php

<?php
  //example taken from https://www.smashingmagazine.com/2011/10/how-to-use-ajax-in-wordpress/
  //generate link
  $nonce = wp_create_nonce("my_user_vote_nonce");
  $link = admin_url('admin-ajax.php?action=my_user_vote&post_id='.$post->ID.'&nonce='.$nonce);
  echo '<a class="user_vote" data-nonce="' . $nonce . '" data-post_id="' . $post->ID . '" href="' . $link . '">vote for this article</a>';

  //accept ajax action 
  add_action("wp_ajax_my_user_vote", "my_user_vote");
  add_action("wp_ajax_nopriv_my_user_vote", "my_must_login");

function my_user_vote() {

   if ( !wp_verify_nonce( $_REQUEST['nonce'], "my_user_vote_nonce")) {
      exit("No naughty business please");
   }   

   $vote_count = get_post_meta($_REQUEST["post_id"], "votes", true);
   $vote_count = ($vote_count == ’) ? 0 : $vote_count;
   $new_vote_count = $vote_count + 1;

   $vote = update_post_meta($_REQUEST["post_id"], "votes", $new_vote_count);

   if($vote === false) {
      $result['type'] = "error";
      $result['vote_count'] = $vote_count;
   }
   else {
      $result['type'] = "success";
      $result['vote_count'] = $new_vote_count;
   }

   if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
      $result = json_encode($result);
      echo $result;
   }
   else {
      header("Location: ".$_SERVER["HTTP_REFERER"]);
   }

   die();

}

function my_must_login() {
   echo "You must log in to vote";
   die();
}
?>