Cannot access /admin/ HTTP ERROR 500

Hi
When I want to access admin panel I get HTTP ERROR 500.
Other parts of the website work fine.
How can I fix this? I’m using ubuntu 16.04

Check the APACHE error logs to debug the issue.

the only thing apache access log shows is this line:

192.168.211.33 - - [02/Jul/2019:23:15:13 +0430] “GET /admin_area/ HTTP/1.1” 500 407 “http://test.com/upload.php” “Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36”

and error.log file is empty