ERR_CONNECTION_REFUSED AWS EC2 when performing GET to backend server

This is my first AWS deployment and I have what is going to be a simple question (but not for me). I would appreciate any help I can get.
I have a React frontend and a backend node server running on an AWS EC2 instance. I have no problem serving the front end to my browser from port 80 (NGINX server) on the public IP address for the EC2 instance but the GET request to the node server on port 3001 returns an error to the console "net::ERR_CONNECTION_REFUSED". Troubleshooting so far;

1. confirmed NGINX and Node servers are running on their proper ports
2. I performed a curl request from the EC2 terminal (curl -X GET http://127.0.0.1:3001/api/users) to the backend server and the information is served successfully from the server/DB but when the request comes from running the app in the client, the connection is refused.
3. I made many changes to the NGINX .conf file (one at a time) including using the public IP vs using localhost (or even 127.0.0.1:3001) for the backend express server but with no success.
4. Made sure to restart the NGINX server to pick up .conf changes.
5. Since I am able to get a response when I use a "curl" request from the VM terminal but not when I request from the client, I wonder if it has something to do with my security group rules. I have Type "HTTPS" on port 443 and "HTTP" on port 80 with "0.0.0.0/0" and "::/0" on both and SSH on port 22 with "0.0.0.0/0". Is there anything that I am missing?

Here is the NGINX .conf info for the servers

   server {
    listen 80 default_server;
        listen [::]:80 default_server;
        server_name _;
        #charset koi8-r;

        #access_log  logs/host.access.log  main;

       location /{
            root /usr/share/nginx/html/aws-thought/client/build;
            index index.html;
            try_files $uri /index.html;
    }
    location /api/ {
        proxy_pass http://127.0.0.1:3001;
    }
}