server {
    listen 127.0.0.1:81;

    root /var/www/your.site.com/public_html;
    index index.php;

    …...

    location / {
        try_files $uri $uri/ /index.php?$args;
    }

    location ~ \.php$ {
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_pass unix:/var/run/php7.2-fpm.sock;
    }
}