After following the instructions from #2609 to setup my external webserver on a different machine with MySQL and NGINX the dynmap is only showing me a black screen (not an empty map, a completely black screen).

Chrome's Developer Tools console shows this error:

Also the site shows this alert:

Could not retrieve configuration: error

I am using dynmap-3.4-beta-3-spigot on spigot 1.18.2 with this configuration.
The MySQL credentials in MySQL_configuration.php do work and have SELECT, INSERT, UPDATE, DELETE, CREATE and INDEX privileges.
Also everything on the gameserver-side seems to be working fine, as the database actually gets filled.

What do the nginx error logs state? Did you install php-fpm and php-mysqli?, Did you set them to the right version in the nginx site conf?

The nginx error logs say this
[error] 9962#9962: *157 connect() failed (111: Connection refused) while connecting to upstream, client: <my ip>, server: map.*, request: "GET /standalone/MySQL_configuration.php HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "map.[my domain]", referrer: "https://map.[my domain]/"

Did you install php-fpm and php-mysqli?

Yes, I did. But is there any way of testing if I made a mistake?

Did you set them to the right version in the nginx site conf?

Honestly I don't know how, as nginx is completely new to me. How exactly would I do that?

It looks like I didn't install php-mysqli properly and forgot to specify the correct version for php-fpm in my nginx config.
Sorry for wasting your time ^^