The FPID cookie is what server-side Google Tag Manager would prefer to use for your Google Analytics 4 tracking. It’s a cookie set in the HTTP response from the server, and it’s flagged as HttpOnly, which means it’s only accessible by a web server running on the domain on which it was set. There’s nothing wrong with the technology, and I do recommend that server-side setups toggle it on by default.

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The FPID cookie in server-side tagging for Google Tag Manager is an HttpOnly, server-managed ID cookie that’s designed to replace the JavaScript-managed _ga cookie used by Google Analytics 4 and Universal Analytics. For more details about the cookie itself, check out my previous article on FPID. In that article, I mentioned one caveat for adopting FPID being the fact that cross-domain tracking will not work. I mean, how could it? FPID is an HttpOnly cookie, which means it’s not available to JavaScript in the browser.

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