tengo problema para adaptar este codigo a antonella. 
function Slug_Register_wpcf_created_facebook() {
    register_api_field('post',
        'wpcf-created_facebook',
        array(
            'get_callback' => 'slug_get_wpcf_created_facebook',
            'update_callback' => 'slug_update_meta_for_api',
            'schema' => null,
        )
    );
}
 
add_action('rest_api_init', 'Slug_Register_wpcf_created_facebook');
 
function slug_get_wpcf_created_facebook($post, $field_name, $request) {
  return get_post_meta($post->id, $field_name);
}
 
function slug_update_meta_for_api($value, $post, $field_name) {
  if (!$value || !is_string($value)) {
    return;
  }
 
  return update_post_meta($post->ID, $field_name, strip_tags($value));
}