I Just install following the The Perfect Server - Debian 10 (Buster) with Apache, BIND, Dovecot, PureFTPD and ISPConfig 3.1 With no problems Please advise. Best Regards,
That's ok like that, you should not use an IP in this field, just select *. If you want to use an IP based vhost e.g. because there are no domain names used in your network or other special reasons why a normal vhost won't work, then you can add the IP under system > Server IP. But as mentioned above, an IP should normally not be used there anymore, just use *.