Stopper 1: NGINX Proxy Mixed Content Error

Installation
3

Stopper 1 solved! No more mixed content messages with any browser (I tried Firefox, Opera and Safari on macOS). This change in Nginx reverse proxy solved also the issue described in my post Problem Responding to a Topic.

As a reference, I’m also posting the updated Nginx conf file:

server {
    server_name forum.igfae.usc.es;

    location / {
        proxy_set_header   X-Forwarded-Proto $scheme;
        proxy_set_header   X-Forwarded-For $remote_addr;
        proxy_set_header   Host $http_host;
        proxy_pass         "http://172.16.57.96";
    }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/forum.igfae.usc.es/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/forum.igfae.usc.es/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server {
    if ($host = forum.igfae.usc.es) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    server_name forum.igfae.usc.es;
    listen 80;
    return 404; # managed by Certbot

}

At the moment of creating this post, Nginx/1.20.1 is running as a reverse proxy on a AlmaLinux release 9.4 (Seafoam Ocelot) server.

Discourse 3.3.0.beta3-dev is running on Docker version 26.1.3, build b72abbb on an Ubuntu 22.04.4 LTS box.

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Thanks to everyone!