After removal of specific PHP version multiple domains hosted in Plesk became not accessible, error 503 is shown in browser

Symptoms

• After removal of specific PHP handler version multiple domains hosted in Plesk became not accessible, "error 503" or "error 500" is shown in the browser.

• On Plesk for Windows following error appears with detailed error reporting enabled:

  500
  FastCGI handler is missing

• The following error message is present in /var/www/vhosts/example.com/logs/error_log:

  No such file or directory: AH02454: FCGI: attempt to connect to Unix domain socket /var/www/vhosts/system/exmple.com/php-fpm.sock (*) failed

• The tab Domains > example.com > PHP Settings is missing.

• Tools & Settings > PHP Settings > PHP version and it shown in a broken state.

• Attempting to run php_handlers_control --reread the following error appears:

  # /usr/local/psa/admin/bin/php_handlers_control --reread
  Domain "example.com": the PHP handler "plesk-php71-fpm" is not registered. It was probably deleted from the server. Register a handler with the same properties and try again.

Cause

PHP version in domain's settings was not changed to a different one before the removal of PHP version.

Resolution

1. Log into Plesk.
2. Reinstall the removed PHP handler version with this instructions, e.g. PHP 7.1.
3. Open Tools & Settings > PHP Settings and check which domains remain assigned to the version needed to be removed.
4. Change PHP version of all domains found on step 3 to other available version, e.g. PHP 8.1.
5. Remove the PHP handler version again with this instructions.