Post meta not updating

I am trying to make a voting system for WordPress.

This is my code in functions.php:

  add_action("wp_ajax_add_votes_options", "add_votes_options");
  add_action("wp_ajax_nopriv_add_votes_options", "add_votes_options");
   function add_votes_options() {
if (!wp_verify_nonce($_POST['nonce'], 'voting_nonce'))
    return;

$postid = $_POST['postid'];
$ip = $_POST['ip'];

$voter_ips = get_post_meta($postid, "voter_ips", true);
if(!empty($voter_ips) && in_array($ip, $voter_ips)) {
    echo "null";
    die(0);
} else {
    $voter_ips[] = $ip;
    update_post_meta($postid, "voter_ips", $voter_ips);
}   

$current_votes = get_post_meta($postid, "votes", true);
$new_votes = intval($current_votes) + 1;
update_post_meta($postid, "votes", $new_votes);
$return = $new_votes>1 ? $new_votes." votes" : $new_votes." vote";
echo $return;
die(0);
    }

This is how I place my vote button and vote count button:

    <?php
// This will display "0 votes" and increase as votes are added
$votes = get_post_meta($post->ID, "votes", true);
$votes = !empty($votes) ? $votes : "0";
if($votes == 1) $plural = ""; else $plural = "s";
echo '<div id="votecounter">'.$votes.' vote'.$plural.'</div>';
?>

<?php
// This will display the vote button and disable it if a cookie has already
// been set. We also add the security nonce here. 
$hasvoted = $_COOKIE['better_votes'];
$hasvoted = explode(",", $hasvoted);
if(in_array($post->ID, $hasvoted)) {
$vtext = "VOTED";
$class = ' class="disabled"';
} else {
$vtext = "VOTE";
$class = "";
}
?>
<a href="javascript:void(0)" id="vote"<?php echo $class; ?>><?php echo   $vtext; ? ></a>
<?php if(function_exists('wp_nonce_field')) wp_nonce_field ('voting_nonce', 'voting_nonce'); ?>

The problem is that it isn’t updating the meta data. It shows 1 votes but doesn’t update the meta data on click. I don’t now what I am doing wrong.