How to enable custom error pages for a domain in Plesk

If Proxy Mode is enabled at Domains > example.com > Apache & nginx Settings, then: go to Domains > example.com > Hosting Settings and enable the Custom error documents setting:

Note: If PHP is run as PHP-FPM application served by Apache, add "ProxyErrorOverride on" to the additional HTTP/HTTPS directives at Domains > example.com > Apache & nginx Settings.

If Proxy Mode is disabled at Domains > example.com > Apache & nginx Settings, add the following content to Additional nginx directives field:

Notes: The Additional nginx directives field is available to Plesk administrator only. If you are a domain owner, please contact your service provider for assistance with configuration of error pages.

To apply these settings for all new domains created under a particular service plan, go to Service Plans > Example Plan > Web Server tab and add the below lines to the Additional nginx directives field.

fastcgi_intercept_errors on;

location ^~ /error_docs/ { root /var/www/vhosts/example.com/; }

error_page 400 /error_docs/bad_request.html;
error_page 401 /error_docs/unauthorized.html;
error_page 403 /error_docs/forbidden.html;
error_page 404 /error_docs/not_found.html;
error_page 405 /error_docs/method_not_allowed.html;
error_page 406 /error_docs/not_acceptable.html;
error_page 407 /error_docs/proxy_authentication_required.html;
error_page 412 /error_docs/precondition_failed.html;
error_page 414 /error_docs/request-uri_too_long.html;
error_page 415 /error_docs/unsupported_media_type.html;
error_page 500 /error_docs/external_server_error.html;
error_page 501 /error_docs/not_implemented.html;
error_page 502 /error_docs/bad_gateway.html;
error_page 503 /error_docs/maintenance.html;