HTTPS POST request fails to nginx/nodejs Bad Gateway

Ive got a rpi2 running node.js with an app configured via .env on port 442. Nginx is configured to serve https with letsencrypt certificate. I tried the node app by itself on http and it responded fine. I tried the served index.html on https on nginx from my mac on the lan and it worked fine. The issue is now that Im trying to combine them.

Im test posting from hurl.it but getting a bad gateway error and the error log on nginx for the site says:

POST /API/switches/sw1?password=123456 HTTP/1.1", upstream: "http://192.168.1.53:442/50x.html", host: "subdomain.domain.com" 2017/04/23 20:08:38 [error] 20424#0: *4 upstream prematurely closed connection while reading response header from upstream, client: 192.168.1.56, server: subdomain.domain.com, request: "GET /aism/ HTTP/1.1", upstream: "http://192.168.1.53:442/aism/", host: "subdomain.domain.com" 2017/04/23 20:08:38 [error] 20424#0: *4 upstream prematurely closed connection while reading response header from upstream, client: 192.168.1.56, server: subdomain.domain.com, request: "GET /aism/ HTTP/1.1", upstream: "http://192.168.1.53:442/50x.html", host: "subdomain.domain.com" 2017/04/23 20:09:25 [error] 20467#0: *1 upstream prematurely closed connection while reading response header from upstream, client: 23.20.198.108, server: subdomain.domain.com, request: "POST /API/switches/sw1?password=123456 HTTP/1.1", upstream: "http://192.168.1.53:442/API/switches/sw1?password=123456", host: "subdomain.domain.com"

Here is my site config:

server {
        listen 80;
        listen [::]:80;
        server_name subdomain.domain.com;
        return 301 https://$server_name$request_uri;
}

server {
        listen 443 ssl;
        listen [::]:443 ssl;
        server_name subdomain.domain.com;

        ssl_certificate          /etc/letsencrypt/live/subdomain.domain.com/fullchain.pem;
        ssl_certificate_key      /etc/letsencrypt/live/subdomain.domain.com/privkey.pem;

        root /www/subdomain.domain.com/aism;
        index index.php index.html index.htm;

        error_page 404 /404.html;
        error_page 500 502 503 504 /50x.html;

        # Error & Access logs
        error_log /www/subdomain.domain.com/logs/error.log error;
        access_log /www/subdomain.domain.com/logs/access.log;

        location / {
                index index.html index.php;
                proxy_pass http://192.168.1.53:442;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection 'upgrade';
                proxy_set_header Host $host;
                proxy_cache_bypass $http_upgrade;
        }
        location ~ /.well-known {
                allow all;
        }
        location /public {
                root /www/subdomain.domain.com/aism;
        }
        location ~ ^/(images/|img/|javascript/|js/|css/|stylesheets/|flash/|media/|static/) {
        }
        location ~ [^/].php(/|$) {
                fastcgi_split_path_info ^(.+?.php)(/.*)$;
                fastcgi_pass unix:/var/run/php5-fpm.sock;
                fastcgi_index index.php;
                include fastcgi_params;
        }
}

What is wrong with my config file for the site?

via marciokoko