Debugging tracking pixels

Practical answers to the questions that come up when ad and analytics numbers don't add up, based on what pixels actually send from live websites.

• Duplicate purchase events: real duplicates vs. normal repeatsSeveral purchase requests for one order are often normal: several pixels, accounts or request formats. How to find a real duplicate and check the order ID.
• GA4 events not showing: check what the tag actually sentWhy a GA4 event or purchase doesn't show in your reports: report delays, consent mode, the wrong measurement ID, first-party tag paths, batched and cancelled requests, and the purchase fields Google requires.
• GA4 purchase sent with a value but no currencyA GA4 purchase with a value but no currency: the keys to look for in the request, what Google's reference says about it, and how to check and fix the tag.
• Why one Google Ads hit shows up as several requestsOne Google Ads conversion can leave the browser as conversion, view-through, CCM and GA4-linked requests. What each carries and why it is not a duplicate.
• Google Ads conversion not recording: what to check in the browserWhy a Google Ads conversion action shows no conversions: the status meanings, what a conversion request looks like, and how to check the account, label, value, currency, order ID and consent your tag actually sends.
• Why Meta and GA4 report different revenueWhy Meta, GA4 and Google Ads report different revenue for the same orders, and how to see the value, currency and order ID each tag sent in the browser.
• Meta Pixel not firing: how to find out whyCheck whether your Meta Pixel sends events: what a Meta Pixel request looks like, the eight usual reasons it doesn't fire or sends the wrong data, and how to check each one in Chrome.
• What tracking pixels actually send: a study of 38 websitesWe opened 38 websites with Pixel Debugger and read every tracking request: how many networks fire, where events go, and what is missing.