add_post_meta doesn’t work

you have pass static postID which is not match at your live server. Please check the ID of post. For good practice pass the dynamic ID as per documentation.

<?php add_post_meta($post_id, $meta_key, $meta_value, $unique); ?> 

$post_id –> The ID of the post to which a custom field should be added.
$meta_key –> The key of the custom field which should be added.
$meta_value –> The value of the custom field which should be added. If an array is given, it will be serialized into a string.
$unique –> Whether or not you want the key to stay unique. When set to true, the custom field will not be added if the given key already exists among custom fields of the specified post.

Or try this logic

<?php
if ( ! add_post_meta( 39, 'overall', 4, true ) ) { 
   update_post_meta( 39, 'overall', 4);
}