Full Answer
Ad blockers intercept outgoing browser requests to known tracking domains—blocking them before they reach Facebook, Google, or TikTok. The WooCommerce order still completes, but the conversion event never fires.
The impact compounds across multiple restrictions: Safari's ITP limits tracking cookies to 7 days, Firefox's Enhanced Tracking Protection blocks requests outright, and EU visitors reject cookie consent banners at 40-70% rates. Combined, these restrictions consistently remove 30-40% of real purchase events from ad platform data—not as a worst case, but as the baseline for any store without server-side tracking.
Server-side tracking bypasses ad blockers because requests originate from your server, not the visitor's browser. Conversion data reaches its destination regardless of what the visitor has installed.