cannot access my api : connection refused while connecting to upstream client

Question

I have a django website deployed in digital ocean. I also considered adding a load balancer since i am expecting a heavy request in my backend. But i keep having an error of connection refused while connecting to upstream.

Here is the actual error:

2023/12/09 15:22:51 [error] 508980#508980: *2462 connect() failed (111: Connection refused) while connecting to upstream, client: 10.116.0.21, server: www.xxxxx.com, request: "POST /api/xxxxx/ask/ HTTP/1.1", upstream: "http://[::1]:8000/api/xxxxx/ask/", host: "xxxxx.com"

I tried to do something like this on my nginx:

upstream http_backend {
    server 127.0.0.1:8000;

    keepalive 16;
}

server {
    listen 80;
    server_name xxx.xxx.xxx.xxx;

    location / {
               try_files $uri @proxy_to_app;
    }
    location @proxy_to_app {
                proxy_pass http://http_backend;
                
                proxy_set_header Host $http_host;
                proxy_set_header X-Real-IP $remote_addr;
                proxy_http_version 1.1;
                proxy_set_header Connection "";               

     }
     location /static/ {
             autoindex on;
             alias /var/www/django-project/main/static/;
     }
     location /media/ {
             autoindex on;
             alias /var/www/django-project/main/media/;
     }

}

why this happens?