Adicionar Metafields ao Rest API do WordPress

add_action( 'rest_api_init', 'create_api_posts_meta_field' );

function create_api_posts_meta_field() {

 // register_rest_field ( 'name-of-post-type', 'name-of-field-to-return', array-of-callbacks-and-schema() )
 register_rest_field( 'posty_tyepe_name', 'metafields', array(
 'get_callback' => 'get_post_meta_for_api',
 'schema' => null,
 )
 );
}

function get_post_meta_for_api( $object ) {
 //get the id of the post object array
 $post_id = $object['id'];

 //return the post meta
 return get_post_meta( $post_id );
}