fop2 user access behind proxy nginx

Dear all,
I tried to publish the fop2 user access online behind a nginx proxy. Here my configuration:

server {
server_name xxx.yyyyyyyy.zzz;

        location / {
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connecion "upgrade"; 
            proxy_pass http://local_ip_address/fop2/;
            proxy_buffering off;
            client_max_body_size 0;
            proxy_connect_timeout  3600s;
            proxy_read_timeout  3600s;
            proxy_send_timeout  3600s;
            send_timeout  3600s;

}

listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/xxx.yyyyyyyy.zzz/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/xxx.yyyyyyyy.zzz/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 ($host = xxx.yyyyyyyy.zzz) {
return 301 https://$host$request_uri;
} # managed by Certbot

       listen 80;
       server_name xxx.yyyyyyyy.zzz;
return 404; # managed by Certbot

}

With this configuration I'm able to reach the fop2 page from the domain xxx.yyyyyyyy.zzz but then it blocks before the login page:
**One moment please
Connecting to server, attempt number : 1
**
Do you have any suggestion? Thank you in advance for your help