Add additional nginx directives globally on plesk

vi /etc/nginx/conf.d/directives.conf

The directives

proxy_send_timeout 1200s;
proxy_read_timeout 1200s;
fastcgi_send_timeout 1200s;
fastcgi_read_timeout 1200s;
proxy_buffers 8 16k;
proxy_buffer_size 32k;
fastcgi_buffers 8 16k;
fastcgi_buffer_size 32k;

Save, close & restart nginx