Symptoms
- Domain is inaccessible with 404 error.
 
 Rewrite rules specified in /var/www/vhosts/example.com/httpdocs/.htaccessfile do not work.
- FPM application served by nginx handler is set in Domains > example.com > PHP Settings .
- In 
 /var/www/vhosts/example.com/logs/error_log
 [error] 20463#0: *1329372 "/var/www/vhosts/example.com/httpdocs/en/component/users/index.html" is not found (2: No such file or directory) 
Cause
When  FPM application served by nginx  is enabled, the website stops using 
  .htaccess
 
  .htaccess
 
Resolution
- Apply 
 /var/www/vhosts/example.com/httpdocs/.htaccess
 If these are CMS-based websites like WordPress or Joomla, apply the steps from the article After switching a WordPress website to FPM served by nginx in Plesk, it fails to load with "404 Not Found" on all pages except start page. Note: rewrite rules should be formed according to nginx syntax. 
- Another solution is to change PHP support for domain from  FPM application served by nginx  to  FPM application served by Apache under  Domains > example.com > PHP Settings.
 
- 
Alternatively, try to convert Apache rules to nginx using htaccess to nginx extension. To install the extension check the article How to manage Plesk extensions (install, disable, remove, update) Note: This extension is experimental. Always check the conversion results manually to prevent possible issues.