Add this code in your child theme functions.php :


  

add_action('template_redirect','wplms_Restrict_non_logged_user_free_unit');

	function wplms_Restrict_non_logged_user_free_unit(){
		if(!is_singular('unit'))
		return;

		$free = get_post_meta(get_the_ID(),'vibe_free',true);
		if(vibe_validate($free) && !is_user_logged_in()){
		  wp_die('Access not allowed');
		}
	}