Please add this code in your wplms-customizer.php file in wplms-customizer plugin :
add_filter('wplms_course_product_id','error_if_not_loggedin',10,2); function error_if_not_loggedin($link,$course_id){ if(!is_user_logged_in()){ $link='?error=login'; return $link; }else{ return $link; } }