Nginx config for redirect from main domain to subdomain

Hi guys,

I have done it. I have upgraded from omv4 to omv5. I have prepared a lot for this. I have moved from nginx-plugin to swag docker. I created backups with clonezilla, restored in virtualbox. trained the upgrade. Reported my issues during upgrade scripts:

https://github.com/dleidert/openmediavault-upgrade/issues/14

https://github.com/dleidert/openmediavault-upgrade/issues/15

https://github.com/dleidert/openmediavault-upgrade/issues/18

https://github.com/dleidert/openmediavault-upgrade/issues/22

So the upgrade went smooth. But even migration to swag was done successfully before upgrade, I get now an internal error in nextcloud. As said it worked before with the same config:

Interner Serverfehler
Der Server konnte die Anfrage nicht fertig stellen.
Sollte dies erneut auftreten, senden Sie bitte die nachfolgenden technischen Einzelheiten  an Ihren Server-Administrator.
Weitere Details können im Server-Protokoll gefunden werden.
Technische Details
Entfernte Adresse: 172.19.0.2
Anfragekennung: mQoutHj9MFZrtANQDwZc

The setup is the following: I had my dyndns domain where I initially hosted nextcloud as main application on main domain. With the migration to swag I wanted to move nextcloud to subdomain as all other applications. To be compatible with old clients, I wanted to redirect main domain to subdomain.maindomain.

What is the best way to do this? I am doing this:

server {
listen 443 ssl http2 default_server;
listen [::]:443 ssl http2 default_server;

server_name _;

include /config/nginx/server.conf;
include /config/nginx/ssl.conf;

return 302 https://nextcloud.maindomain$request_uri;
}

in another file:

server {
listen 443 ssl http2;
listen [::]:443 ssl http2;

server_name nextcloud.*;

include /config/nginx/server.conf;
include /config/nginx/ssl.conf;

client_max_body_size 0;

location / {
include /config/nginx/proxy.conf;

resolver 127.0.0.11 valid=30s;

set $upstream_app nextcloud;
set $upstream_port 80;
set $upstream_proto http;
proxy_pass $upstream_proto://$upstream_app:$upstream_port;

proxy_max_temp_file_size 2048m;
}
}

Maybe this is not the problem at all...could really need your help. Dont want to go back as everything else is working just as it should.

Update: issue with nc was solved, but help with nginx and the question above still welcome!