This field is meant for a plain Google tag ID (G-XXXXXXX) when you do not use Tag Manager. In the current version, however, this is a real bug: the website header checks for a differently-named setting that is never set anywhere in the admin panel, so whatever you enter here is never injected into your pages — it has no effect. Use Google Analytics Tracking Number (which accepts a G- measurement ID) or Google TagManager instead, and report this to Sprwt support if you specifically need a tag-only setup.