Nginx add_header

fail1.conf

# Nginx will fail to start and will throw an error like this:
# Reloading nginx configuration: nginx: [emerg] "add_header" directive is not allowed here in /etc/nginx/sites-enabled/fail1.conf:39

server {

  listen 8080 default;
  server_name _;

  root /var/www/html ;

  if ($http_host = 'evan.com') {
    add_header 'X-Evan-A' '1';
  }
  
  location / {

  }

}

ok1.conf

# This works

server {

  listen 8080 default;
  server_name _;

  root /var/www/html ;
  
  add_header 'X-Evan-A' '1';
  
  location / {
  
  }

}

ok2.conf

# This works

server {

  listen 8080 default;
  server_name _;

  root /var/www/html ;
  
  location / {
    if ($http_host = 'evan.com') {
      add_header 'X-Evan-A' '1';
    }
  }

}

ok3.conf

# This works

server {

  listen 8080 default;
  server_name _;

  root /var/www/html ;
  
  location / {
    add_header 'X-Evan-A' '1';
  }

}