Question Pointing other users domains to mine

[DanPha]

Server operating system version

Ubuntu 22.04

Plesk version and microupdate number

18.0.58 #2

Hi,

I would like to set it up so other users could point their domains at mine eg:
client.clientsite.com -> client.mysite.com

My extra nginx file looks like so:
server_name *.mysite.com;
location ~ / {
proxy_pass http://localhost:3000
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_redirect off;
}

I've tried:
server_name _;

But this does not work, this also breaks the subdomains for mysite.com. It does kind of work with:
server_name *.clientsite.com *.mysite.com

But this would not be a viable option as the website grows. The *.clientsite.com also ends up showing www.mysite.com instead of client.mysite.com

The SSL for the clients subdomains is all setup via cloudflare and works fine, its just this nginx problem which I cannot get my head around.

Thanks