Piwik on intranet server

I have installed piwik on an intranet server (vpn). The website is accessible via http://x.x.x.x/intranet

Should I set this address as my website or something like “localhost”?

I have tried both, then I installed the plugin in wordpress and it keeps displaying this error:

An error occured: Please check URL and auth token. You need at least view access to one site.

in the wordpress plugin you must set the URL to Piwik, not to your website