NGINX two domain in one server - nginx

Question

I want to configure nginx on my ubuntu 20 for the main domain and subdomain.
server {
location / {
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_pass http://127.0.0.1:3000;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
}
listen [::]:443 ssl ipv6only=on ;
listen 443 ssl;
ssl_certificate /etc/letsencrypt/live/maindomain.com/fullchain.pem;
ssl_certificate_key /etc/letsencrypt/live/maindomain.com/privkey.pem;
include /etc/letsencrypt/options-ssl-nginx.conf;
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;
}
server {
if ($host =maindomain) {
return 301 https://$host$request_uri;
}
listen 80 ;
listen [::]:80 ;
server_name maindomain.com
return 404;
}
And this domain works, but I want to launch another subdomain here, and here I already ran into a lot of problems (including cerbor 443 port, etc.) .
Both projects are located in the folder home/webdev/main domain and home/webdav/subdomain. Both projects are on next js . The database of the first project and the decker hung on port 3000, 5432:5432 and 8080:8080. Subdomain 3001 is the port I want , "5433:5433" and 8081:8081. I 'm new to nginx , tried it like this.
server {
location /subdomain {
root home/webDev;
# First attempt to serve request as file, then
# as directory, then fall back to displaying a 404.
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_pass http://127.0.0.1:3001;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
}
}
Or
server {
# Binds the TCP port 80.
listen 81;
# Defines the domain or subdomain name.
# If no server_name is defined in a server block then
# Nginx uses the 'empty' name
server_name maindomain/subdomain.com;
# Redirect the traffic to the corresponding
# HTTPS server block with status code 301
return 301 https://$host$request_uri;
}