You will want to make the following changes to your add_custom_field_automatically function. First, we will need to add the global $post; as we will need the $post variable inside the function scope. You do this with a comma. more on variable scope here. add_action(‘publish_post’, ‘add_custom_field_automatically’); function add_custom_field_automatically($post_ID) { global $wpdb, $post; if(!wp_is_post_revision($post_ID)) { add_post_meta($post_ID, ‘field-name’, … Read more