Hey everyone, I fixed the error and here is the solution:
the nginx settings were missing:
location / {
proxy_pass http://localhost:8000;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Proto $scheme;
client_max_body_size 20m;
}