how to reproduce. In a ubuntu 20.04 perfect apache server with ispconfig 3.2.3 install diferrent php versions following (customised) guide with sury.org. Configure a site to use php(some) with fpm and then change to php(another) fpm then visit site and it shows ERROR 503 - Service Unavailable! the problem is solved if i go to console and command systemctl restart php(another)-fpm The problem doesn't occur if i go php(some) fpm->php another cgi->php another fpm. So my guess is in one scenario one systemctl restart php(another)-fpm is missing. Thanks!