How to connect securely between Node and Vue on one Droplet?

I set up SSL with Let’s Encrypt and it works as it should. On my droplet there is Nginx as reverse proxy and forwards the request to my frontend on port 3000 --> it works!. But my frontend does fetch data from my backend with Node on port 8080. My domain is secured and uses the HTTPS protocol but in my private network (frontend + backend) I cannot establish a communcation between them. I got a Chrome Dev Tools error:

GET http://127.0.0.1:8080/api/videos/all net::ERR_CONNECTION_REFUSED

I assume there is a secure connection expected but I don’t know how to set it up. I tried to use https://127.0.0.1:8080 but it does not work as well.

Nginx-config:

server {

        root /var/www/html;

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

        server_name my-domain.com www.my-domain.com;

        location / {
                proxy_pass http://localhost:3000;
                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;
        }

    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/my-domain.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/my-domain.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot


}


server {
    if ($host = www.my-domain.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


    if ($host = my-domain.com) {
        return 301 https://$host$request_uri;
    } # ma
}