Nginx has conflict with an application running on 443

In MacOS, I usually run my project in localhost by sudo PORT=443 HTTPS=true ./node_modules/.bin/react-scripts start. As a result, https://localhost/#/start works in a browser.

Now, to run third-party authentications in localhost, I need to run nginx. Here is my /usr/local/etc/nginx/nginx.conf:

worker_processes  1;

events {
    worker_connections  1024;
}

http {
    include       mime.types;
    default_type  application/octet-stream;

    sendfile        on;

    keepalive_timeout  65;

    upstream funfun {
        server 178.62.87.72:443;
    }

    server {
        listen              443 ssl;
        server_name localhost;
        ssl_certificate /etc/ssl/localhost/localhost.crt;
        ssl_certificate_key /etc/ssl/localhost/localhost.key;
        ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
        ssl_prefer_server_ciphers on;
        ssl_session_timeout 1d;
        ssl_stapling off;
        ssl_stapling_verify off;
        add_header Strict-Transport-Security max-age=15768000;
        add_header X-Frame-Options "";
        proxy_ssl_name "www.funfun.io";
        proxy_ssl_server_name on;

        location ~ /socialLoginSuccess {
            rewrite ^ '/#/socialLoginSuccess' redirect;
        }

        location ~ /auth/(.*) {
            proxy_pass  https://funfun/10studio/auth/$1?$query_string;
            proxy_set_header Host localhost;
        }

        location / {
            proxy_set_header    Host                $host;
            proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
            proxy_set_header    X-Forwarded-Proto   $scheme;
            proxy_set_header    Accept-Encoding     "";
            proxy_set_header    Proxy               "";
            proxy_pass          https://localhost/;
            # These three lines added as per https://github.com/socketio/socket.io/issues/1942 to remove socketio error
            proxy_http_version 1.1;
            proxy_set_header   Upgrade $http_upgrade;
            proxy_set_header   Connection "upgrade";
        }
    }
    include servers/*;
}

However, launching the nginx returns me the following errors:

$ sudo nginx
nginx: [emerg] bind() to 0.0.0.0:443 failed (48: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (48: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (48: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (48: Address already in use)
nginx: [emerg] bind() to 0.0.0.0:443 failed (48: Address already in use)
nginx: [emerg] still could not bind()

It seems that, nginx has conflit with the app running on 443. Does anyone know why?

Additionally, could anyone tell me what’s the purpose of the block location / { ... } in my nginx configuration file?