504 Gateway Timeout - [proxy_fcgi:error] - register form PrestaShop

When registering a customer in PrestaShop, I receive:

Gateway Timeout
The gateway did not receive a timely response from the upstream server or application.
I have

cat /home/admin/web/x./logs/growshop.org.error.log
[Tue Feb 13 09:30:13.211778 2024] [proxy_fcgi:error] [pid 65212:tid 140707608057600] (70007)The timeout specified has expired: [client] AH01075: Error dispatching request to : (polling), referer: https://x.x/pl/index.php?controller=registration

I had a similar problem [SOLVED] 504 Gateway Timeout - [proxy_fcgi:error] - contact form PrestaShop.
I solved it using the way Webmail with Gateway Timeout - #12 by jlguerrero.
I also enlisted the help of Required parameters: memory_limit (missing description) - General topics - PrestaShop Forums.

Where might the problem be?