Oh man, I've been there before. That HTTP 500 error can be a real pain. Here's what I did when I faced something similar on my CentOS 7 server with Plesk 18 (Obsidian):
Check Logs: I started by looking at the logs. Plesk keeps its logs in /var/log/plesk/panel.log, and for the web server, it's either /var/log/httpd/error_log for Apache or /var/log/nginx/error.log for Nginx. These files can give you some clues about what's going wrong.
Permissions: I made sure all the file and folder permissions were set right. Sometimes, if they're off, it can cause issues.
Disk Space: I checked to see if my server's disk was full. A full disk can cause all sorts of weird problems.
Restart Services: I tried restarting the Plesk and web server services. You can do this with these commands:
bash
service psa restart
service httpd restart # For Apache
service nginx restart # For Nginx
Check for Corrupted Files: I ran Plesk's repair utility to see if there were any corrupted files. You can do this with:
css
plesk repair all -y
PHP Settings: I checked my PHP settings and the PHP error log to see if there were any issues there, especially if I had made any recent changes.
Disable Extensions: I had some third-party extensions installed, so I tried disabling them to see if that fixed the issue.
If none of that works, it might be time to reach out to Plesk support or your hosting provider for some extra help.