Adds a custom field (also called meta-data) to a specified post which could be of any post type. A custom field is effectively a key–value pair

Parameters supported : post_id, meta_key, meta_value

Syntax:

[query.add_non_unique_post_meta post_id AND meta_key AND meta_value /]

Example:

[query.add_non_unique_post_meta post_id="575512" meta_key="poetry-comments-count" meta_value="34" /]