How to remove standard 503 nginx error?

Question

Nginx

In general, I transferred the site to WP from LEMP to the same LEMP. Everything is set up, but there is one problem. There is this plugin for prevention https://ru.wordpress.org/plugins/maintenance/
which causes a 503 error for search engines. Everything worked fine on the old one and this page was from this plugin. on the new one, the standard error 503 comes out. If you remove the html of this error, it goes to 500.
Maybe someone came across it? how to remove the standard nginx 503 error call?