PVECM: can't connect to 8006 - error 500

[rootless]

Hi

I have an existing Proxmox server and would like to add a second root server as a node. Since these two servers must be on the same network according to the instructions, I have established a VPN connection between the two servers. Both servers can communicate with each other (Ping, SSH...) and both are on the newest Proxmox version.

pve-manager/5.2-6/bcd5f008 (running kernel: 4.15.18-1-pve)

As soon as I want to add the second node with the following command:

pvecm add 10.1.1.1

After entering the root password, I get the following error:

Etablishing API connection with host '10.1.1.1'
500 500 Can't connect to 10.1.1.1:8006

I suspect the problem in the configuration of NGINX, but can't figure out how to solve it. When I try to check the port via Telnet from the node ("telnet 10.1.1.1 8006"), I get the following error, but I don't see any indication of the actual problem:

Trying 10.1.1.1...
Connected to 10.1.1.1.
Escape character is '^]'.
Connection closed by foreign host.

The nginx.conf configuration looks like this:

upstream proxmox {
    server "proxmox.example.com";
}

server {
    listen 80;
    server_name proxmox.example.com;
    return 301 https[:]//$host$1$request_uri;
}

server {
    listen 443 http2 ssl default_server;
    server_name proxmox.example.com;
    ssl on;
    ssl_certificate /etc/letsencrypt/certs/proxmox.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/certs/proxmox.example.com/privkey.pem;
    proxy_redirect off;
    location / {
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_pass https[:]//localhost:8006;
        proxy_buffering off;
        client_max_body_size 0;
        proxy_connect_timeout  3600s;
        proxy_read_timeout  3600s;
        proxy_send_timeout  3600s;
        send_timeout  3600s;
    }
}

server {
    listen 80;
    #prevent access via the server public IP addresse
    server_name AA:BB:CC:DD;
    return 403;
}

Unfortunately, I don't know what to do. Are there any ideas?

[] had to remove the "links" because i am a new member