Nginx no resolver defined to resolve domain.com - what's wrong?

Question

Nginx

I want to make a proxy for the mobile version

server {
        listen 80;
        server_name m.domain.com;
        location / {
                proxy_pass http://domain.com/mobile/$request_uri;
        }
}

In the logs I get no resolver defined to resolve domain.com.
A friend has this configuration.
What can be wrong?
Thank you.

Answer 1

Either write
Or (if you don't trust Google):
Well, the most correct thing is to register the ip address instead of domain.com and pass the Host header to the backend:
proxy_set_header Host $host;