How to configure apache on a port other than 80?

Question

Apache HTTP Server

Bottom line:
Apache works correctly on port 80, and when you change it to 81, it sends it to all sites with php - forbidden
details:
there is a server with sites, everything is spinning on Apache
now it is necessary to send some sites through nginx
change the Apache port from 80 to 81 (change in apache2.conf listen) we
hang the configured nginx on 80
we get it for all sites running on php - Forbidden
if you go to the direct site.ru: 81 it is also forbidden
if the Apache changes the port back to 80 everything works correctly
how to make apache work correctly on 81 port?

Answer 1

Believe it or not, Forbiden is Apache's answer, which means it works, it's just set up crookedly. Config to the studio or look for yourself where deny stands.