Hey, thanks for the response @KFSys. I have two server blocks in sites-available linked in sites-enabled at the moment:

This is my server block for the rails_site (the one that works but is also where my subdomain blog.mysite.com is pointing).

server {

        server_name rails_site.com www.rails_site.com;
    listen 80 default_server;
    listen 443 ssl;

    if ($scheme != "https") {
        return 301 https://rails_site.com$request_uri;
    }

    if ($host = www.ciaoplace.com) {
        return 301 https://rails_site.com$request_uri;
    }

        root /srv/rails_site/current/public;

        passenger_enabled on;
        passenger_app_env production;

        passenger_force_max_concurrent_requests_per_process 0;

        client_max_body_size 40m;

        location ~ ^/(assets|packs) {
                expires max;
                gzip_static on;
        }

   # certbot stuff (paths modified when posted here)

    ssl_certificate path/fullchain.pem; # managed by Certbot
    ssl_certificate_key privkey.pem; # managed by Certbot

}

The second was generated by Ghost when I installed it on the server:

server {
    listen 80;
    listen [::]:80;

    server_name blog.mysite.com;
    root /srv/blog/system/nginx-root; # Used for acme.sh SSL verification (https://acme.sh)

    location / {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header Host $http_host;
        proxy_pass http://127.0.0.1:2368;

    }

    location ~ /.well-known {
        allow all;
    }

    client_max_body_size 50m;
}