504 after form submission?

Question

Nginx

there is a contact form on the site
after using it, everything freezes, loading appears on the site icon, the send button is "sent"
as a result, everything hangs for a while and I get a 504 error,
but the message from the site still goes to the address

2019/12/03 06:55:40 [error] 22350#22350: *21911 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 8.1.3.9, server: site.ru, request: "POST / HTTP/2.0", upstream: "fastcgi://unix:/$

timeouts cost 150 each...
submitting a php form is not a tricky business, why should anything ever hit a timeout, what's the problem?

Answer 1

If the form is simple, and the timeouts are 150, then the problem is not with Nginx, but with the backend processing the form.