"Secure Connection Failed" Error when trying to connect to HTTPS

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UPDATE: I looked through some old notes of when I got Discourse working on a previous server (although Nginx was on that same server). I followed Step 3 of this guide for generating the Let's Encrypt Key/Cert pair. Here is my Nginx conf file:

server {
    listen 80; listen [::]:80;
    server_name board.epochgames.co.uk;

    # Redirect all HTTP requests to HTTPS with a 301 Moved Permanently response.
    return 301 https://$host$request_uri;
}

server {
    # The IP that you forwarded in your router (nginx proxy)
    listen 443 ssl http2; listen [::]:443 ssl http2;

    # Make site accessible from http://localhost/
    server_name board.epochgames.co.uk;
    root /home/lighttpd/http;

    # SSL config
    # ssl on;
    ssl_certificate /etc/nginx/ssl/fullchain1.pem;
    ssl_certificate_key /etc/nginx/ssl/privkey1.pem;
    ssl_session_timeout 1d;
    ssl_session_cache shared:SSL:50m;
    ssl_session_tickets off;
    # include /etc/nginx/snippets/ssl.conf;

# The internal IP of the VM that hosts your Apache config
    set $upstream board.epochgames.co.uk;

    location / {
        # proxy_pass_header Authorization;
        proxy_pass http://$upstream;
        proxy_set_header Host $host;
        proxy_set_header X-Forward-Proto $scheme; #X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_http_version 1.1;
        # proxy_set_header Connection "";
        # proxy_buffering off;
        # client_max_body_size 0;
        proxy_read_timeout 90; #36000s;
        proxy_redirect http://$upstream https://board.epochgames.co.uk;
    }
}

And here are the results after restarting Nginx:

Domain Name What Happens?
http://board.epochgames.co.uk/ Redirects to https://board.epochgames.co.uk/
https://board.epochgames.co.uk/ “Apache2 Ubuntu Default Page" It's identical to THIS page.
http://board.epochgames.co.uk:2045 “ Congratulations, you installed Discourse! ” (the message I expect to see)
https://board.epochgames.co.uk:2045 “ Secure Connection Failed: An error occurred during a connection to board.epochgames.co.uk:2045. SSL received a record that exceeded the maximum permissible length. Error code: SSL_ERROR_RX_RECORD_TOO_LONG”
Let me make this clear: Apache is not installed on either the Nginx VM nor the Discourse VM! Ran an apt purge apache on both and the "apache" package was not found!

So only difference now is https://board.epochgames.co.uk/. I remember running into the Apache Default Page before in a previous install of Discourse, but can't remember what fixed it. Any ideas?

Thanks for the link @JuergenAuer, but I don't believe this site is very straight-forward. So I sought out THIS guide to explain cerbot installation and went through the following steps:

sudo add-apt-repository ppa:certbot/certbot
sudo apt-get update
sudo apt-get install python-certbot-nginx
sudo vim /etc/nginx/sites-available/default

Added boards.epochgames.co.uk to the default file. nginx -t brought up an error about port 80 already being called, so I commented out server { listen 80; ... } section in the board.epochgames.co.uk Nginx conf file. Now nginx -t reports no errors.

So now I ran certbot --nginx, where I "reinstalled" the existing certificate for board.epochgames.co.uk (and chose the Redirect option). Got the Congratulations! You have successfully enabled https://board.epochgames.co.uk message, restarted Nginx and tried out the site URLs again ... same results as before certbot install.

I don't think its the keys/certs anymore? I'm not really sure what to try next. I'm tempted to try installing Nginx straight to the Discourse VM itself and running through the Let's Encrypt key/cert process on that server, see if that does any good. Any ideas?