I can't get past the Email setup

Hi, im new to this Forum, so please excuse me if I do something wrong.

I am trying to setup selfhosted Invoice Ninja on Ubuntu 20.04. Everytime I get to the setup screen, everything works except for the email setup. I get everytime the Error “Oops, looks like something isn’t correct!” and in the console it says “504 Gateway timeout”

Ninja Version: v5.7.63
laravel.log: [2023-12-28 22:39:46] production.INFO: db fails
this is the only entry in the log, there is nothing more
I am using an root server

Things I tried:
3x fresh reinstall:
Debian 9
Ubuntu 20.04
Ubuntu 22.04
MariaDB on other server.
2 Email Providers

Changes:
I was using Certbot to get an SSL Certificate for nginx

I hope I gave every information and that some can help me.
Thanks!

Hi,

@david do you have any suggestions?

Is there maybe another log directory where I can search for an error? I don’t know what to do.

There may be more info in the web server error logs.

Hello,
I am slowly loosing hope. This is what I found in the error log from nginx:
2024/01/06 21:45:13 [error] 501#501: *1 upstream timed out (110: Unknown error) while reading response header from upstream, client: xxx.xxx.xxx.xxx, server: invoice.xxxxxx.tld, request: "POST /setup/check_mail HTTP/2.0", upstream: "fastcgi://unix:/run/php/php-fpm.sock", host: "invoice.xxxxxxxx.tld", referrer: "https://invoice.xxxxxxx.tld/setup"

I have tried to change the fpm path from /run/php/php8.1-fpm.sock to /run/php/php-fpm.sock.
The fpm service is 100% running

I have no idea what to do.
Can somebody help me? Maybe @david?

Maybe this post will help, they faced the same error.