register_meta and the REST API
In the year since 4.8, confusion about how to properly expose meta information through the REST API has been one of the most prevalend issues we've seen in support posts and tickets.
Most developers try to use
show_in_rest => true; unfortunately
register_meta works on object types, not subtypes, so you cannot pass a custom post type name into
register_meta like you can with
register_rest_field. Worse, if you register meta for the type
'post', then that meta key is registered not just for core posts, but for every single custom post type. Meta almost never applies across all post types, so this behavior forces developers to use
register_rest_field for REST API data modeling instead of taking advantage of the API's built-in meta handling.
there is no way to and this behavior makes it impossible for a developer to register meta that is specific to their single post type. and requires any REST API data modeling to use