Your WordPress website may be displaying a 500 error due to a misconfiguration, the installation of a plugin or theme that is not compatible with your current version, or due to excessive PHP memory consumption.
Identify the cause of the problem
If the 500 error occurs after installing a theme or plugin, disable it and then retry loading the page that was displaying the 500 error.
If you have not added a theme or plugin recently, it is possible that your site requires more PHP memory to function.
To identify the problem more accurately, log into your Plesk interface, go to the "Logs" section and select the "Apache Error" and "Nginx Error" filters to display only error messages.
Insufficient PHP memory
In your Plesk interface logs, if you see a message like this one, it tells you that the PHP memory quota (memory_limit) is not sufficient and that a theme or plugin is trying to use more memory:
PHP message: PHP Fatal error: Out of memory (allocated 83886080) (tried to allocate 20480 bytes) in [/mywebsite.ch/httpdocs/wp-includes/class-wp-fatal-error-handler.php]
In this case, you can subscribe to an option to obtain a higher PHP memory quota. The subscription is done through the client area.
If you are unable to identify the cause of the 500 errors on your WordPress website, please feel free to open a support ticket so that we can assist you in resolving the issue.