The latest articles on DEV Community by RAMO (@elias_0549e0e2ef8cf6ad89a). https://dev.to/elias_0549e0e2ef8cf6ad89a https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.us-east-2.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F4225815%2F585211d9-cca0-479d-9f73-ab0c4bd4be82.png https://dev.to/elias_0549e0e2ef8cf6ad89a en RAMO Wed, 04 Nov 2026 17:06:14 +0000 https://dev.to/elias_0549e0e2ef8cf6ad89a/what-broke-when-we-counted-conversions-twice-and-the-boring-test-that-fixed-it-d10 https://dev.to/elias_0549e0e2ef8cf6ad89a/what-broke-when-we-counted-conversions-twice-and-the-boring-test-that-fixed-it-d10 <p>We run a small Israeli tools and home-improvement store, <a href="https://ramo.co.il" rel="noopener noreferrer">ramo.co.il</a>, on Next.js and Vercel. A few weeks ago our ad dashboards said we were doing great. Our bank account disagreed.</p> <p>The cause was dull: the purchase event fired twice on the thank-you page. Once on the first render, and again after a client-side navigation re-mounted the component. Google Ads and Meta both happily counted two sales, and the bidding algorithms started paying more for traffic that wasn't converting as well as they thought.</p> <h2> How we found it </h2> <p>Not from the dashboards. We opened the network tab, finished a test order and watched two identical <code>purchase</code> hits go out a few hundred milliseconds apart. That was the whole investigation.</p> <h2> The fix </h2> <ol> <li>Fire purchase events from one place only, keyed by order ID.</li> <li>Store the order ID in <code>sessionStorage</code> after sending, and skip if it's already there.</li> <li>Pass the same <code>transaction_id</code> / <code>event_id</code> to every platform so they can dedupe on their side too.</li> </ol> <h2> The test that keeps it fixed </h2> <p>The real win was a Playwright test that runs before every deploy. It loads a product page, adds to cart, completes a test checkout and counts outgoing requests per platform. If any tag fires zero times or more than once, the deploy is blocked.</p> <p>It takes about a minute to run and it has already caught one regression from an unrelated refactor.</p> <p>If you sell anything online, check your purchase event today. Place a test order with the network tab open. It's five minutes, and it might explain why your ROAS looks better than your revenue.</p> webdev nextjs ecommerce testing