There are two new custom templates available in server-side Google Tag Manager. These templates have been designed to facilitate Piwik PRO tracking in a server-side container. Piwik PRO Client -> This Client template interacts with the Piwik PRO JavaScript tracker and lets you route Piwik PRO tracking through a server-side GTM container. GitHub repo. Piwik PRO -> The tag template works in unison with the Piwik PRO Client, forwarding the hits to the Piwik PRO endpoint.