I reinstalled nginx and re-added that directive to the new configutation file. Now this happens:

>> sudo nginx
>> nginx: [emerg] bind() to 10.0.1.187:2525 failed (49: Can't assign requested address)

In regards to the example given above:

server {
listen some_ip:some_port default;

location / {
add_header X-h1 h1;
add_header X-h2 "h2 h2";
add_header X-h3 h3;
add_header X-h4 h4;
add_header X-h5 h5;
add_header X-h6 "h6 h6";
add_header X-h7 h7;
proxy_pass http://backend;
}
}

some_ip:some_port is the site that I'm trying to pass the headers to. For http://backend, I'm using "http://127.0.0.1"

Any help would be appreciated.