Think I'm missing something with mb-user-meta.

I have the following code hooked into the rwmb_meta_boxes filter.

     $meta_boxes[] = array(
            'title'  => 'Max Things',
            'type'   => 'user', // THIS: Specifically for user.
            'fields' => array(
                array(
                    'name' => 'Max thingsAllowed',
                    'id'   => 'max_things_allowed',
                    'type' => 'number',
                ),
            ),
        );

        return $metaboxes;

However, it's not showing up on the WP user profile screen in wp-admin. So I think I'm missing something very fundamental.

The mb-user-meta add-on is activated. I even tried activating the mb-user-profile add-on.

Ideas?