Domain Mapping plugin - when I click map domain, nothing happens.

Installed the plugin, moved the sunrise.php file to the appropriate folder.

Now I'm trying to actually map a domain to a WP subdomain instance.

My wp install is a multisite, subdomain setup running on a dedicated server.

When I try to map example.com to sub.domain.com I click the Map Domain button, the page refreshes, but nothing actually changes.