Nginx Angular App can’t access REST API on localhost in production

I've searched around quite a bit and still haven't found a solution that works for my issue…

We have a NodeJS application that is an Express app exposing a REST API on localhost:3000. We also have an AngularJS application that is built (ng build –prod) and then served by Nginx. On a local machine, everything works fine. When I put it in to production, the Angular app can't access any of the API endpoints.

XHR Headers Information

Developer Console Output

Initially, I thought this could be a CORS problem, so I adjusted my Nginx configuration to be as follows:

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


        root /var/www/html;

        index index.html index.htm index.nginx-debian.html;

        server_name _;

        location / {
                if ($request_method = 'OPTIONS') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';

        add_header 'Access-Control-Max-Age' 1728000;
        add_header 'Content-Type' 'text/plain; charset=utf-8';
        add_header 'Content-Length' 0;
        return 204;
     }
     if ($request_method = 'POST') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
        add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
     }
     if ($request_method = 'GET') {
        add_header 'Access-Control-Allow-Origin' '*';
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range';
        add_header 'Access-Control-Expose-Headers' 'Content-Length,Content-Range';
     }
        }
}

That didn't solve the problem. There is no information in any of the Nginx logs, and I can successfully access the REST API via curl when logged in to the server. I'm stuck. Any help is appreciated.