How do I find the website ID, also called idSite or Site ID?
Every added in Piwik PRO website has its own ID. To find out its value just click on left upper corner Menu, choose the Administration from the drop-down list and press on the Websites & apps. Choose any website that you are interested in and its ID will be visible right under the name of the page:
Piwik PRO Standalone uses numeric siteID while Piwik PRO Analytics Suite uses new hexadecimal UUID.