The message "500 Internal Server Error" comes from the Apache web server.
The most common cause of this problem is an error in the app's .htaccess file.
If you see this error, you should look in your app's Apache error log to find out more details of the specific error. The app's Apache error log is located at
/srv/users/serverpilot/log/APPNAME/APPNAME_apache.error.log