Add meta box to custom post

Hi I have a meta box I’m trying to enable in custom post types but I can’t see what’s wrong with the following code. Can anyone help?

Thanks

function meta_box() {
	if ( function_exists( 'get_post_types' ) ) {
		$post_types = get_post_types( array(), 'objects' );
		foreach ( $post_types as $post_type ) {
			if ( $post_type->show_ui ) {
				add_meta_box( 'Publish to twitter', 'twitter', array( 'add_twitter_metabox', 'noindex_option_fill' ), $post_type->name, 'side' );
				add_meta_box( 'Add to the slider', 'slider', array( 'add_slider_metabox', 'noindex_option_fill' ), $post_type->name, 'side' );
			}
		}
	} else {
	add_meta_box( 'twitterbox', __('Publish to twitter', 'twitter'), 'add_twitter_metabox', 'post', 'normal', 'high');
	add_meta_box( 'sliderbox', __('Add to the slider', 'slider'), 'add_slider_metabox', 'post', 'normal', 'high');
	}
}