Why am I getting invalid parameter for a variable I defined in map?

I'm trying to define whitelisting for certain domain names on my server. I've figured out a way to do this using the map context but now I'm getting an invalid parameter "$whitelist" for a variable that I have defined in the map context. I already tried this method before, and it's worked, but now I'm suddenly getting an error. I'm not sure why that's the case though.

map $http_host $whitelist {
  default 0;
  "~^(?<subdomain>\w+)\.(?<domain>domain-name\.example\.com)$" $domain;

  # whitelist domains
  whitelist1 example.com;
  whitelist2 subdomain.example.com;
}

server {
  listen 80;
  resolver 127.0.0.11 ipv6=off;
  proxy_intercept_errors on;


  # error_page 400 403 = @fallback;
  if ($whitelist = 0) {
    return 403;
  }

  location /v1/ {

    allow $whitelist;
    deny all;
  }

  location @fallback {
    return 400;
}