It seems to be a problem with the domain. Is it accessible?

sudo certbot –nginx –agree-tos –redirect –hsts –staple-ocsp –email ajsladek@protonmail.com -d Netdata
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Error while running nginx -c /etc/nginx/nginx.conf -t.

nginx: [emerg] invalid parameter “server_name” in /etc/nginx/conf.d/netdata.conf:12
nginx: configuration file /etc/nginx/nginx.conf test failed

The nginx plugin is not working; there may be problems with your existing configuration.
The error was: MisconfigurationError(‘Error while running nginx -c /etc/nginx/nginx.conf -t.\n\nnginx: [emerg] invalid parameter “server_name” in /etc/nginx/conf.d/netdata.conf:12\nnginx: configuration file /etc/nginx/nginx.conf test failed\n’)

My netdata.conf:

upstream backend {
# the Netdata server
server 127.0.0.1:12999;
keepalive 64;
}

server {
# nginx listens to this
listen 80

# the virtual host name of this
server_name C4.netfree;

location / {
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-Server $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://backend;
proxy_http_version 1.1;
proxy_pass_request_headers on;
proxy_set_header Connection “keep-alive”;
proxy_store off;
}
}