Error 500, how to debug if no any logs?

Hello

One of client's side starts giving error 500 but no any logs neither in /usr/local/apache/logs nor /usr/local/apache/domlogs/, same no any info in /var/log/nginx

Page is located in subdomain, there is some access logs messages and some older error messages for this subdomain but no any new line in error logs, just give

500 Server Error
Oops, something went wrong.
Try to refresh this page or feel free to contact us if the problem persists.


Need urgent help. Please any advice for debug.

I'm not familiar with PHP programming myself, how to enable some debug maybe?

I found and fixed the error this time, but would be great to locate a simple way to debug such errors