No host name in browser Nginx

Question

I'm having a problem with nginx server. When I deploy it and type my hostname in the broker window it will find the page, but it will display IP, not the host name. I tried few things and it always fails. It is strange because I used this before and worked.

I can add that I'm using it as a reverse proxy. DNS correctly redirects to IP. But no hostname is shown. I tried this on AWS EC2 and on digital ocean.

My basic conf is:

server {
    listen 80;
    listen [::]:80;
    server_name hostname.com;

    location / {
                    proxy_pass http://api:8000/index;
                    proxy_set_header Upgrade $server_name;
                    proxy_set_header Host $server_name;
    }
}