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Pixel Helper Limitations

The Facebook Pixel Helper browser extension is a useful debugging tool, but there are scenarios where it will not show an event even though the event was correctly delivered to Facebook. This page explains the most common case.

Events fired during a page redirect

Some events — most notably CompleteRegistration — are fired immediately after an action that triggers a page redirect. In PrestaShop, after a customer completes registration they are automatically logged in and the browser is redirected to the home page.

What happens technically

  1. The PS hook fires and the Conversions API (CA) event is sent server-side — this is unaffected by any browser navigation.
  2. The frontend script calls fbq('track', 'CompleteRegistration') on the same page load.
  3. The page starts navigating away (redirect).
  4. The Facebook pixel SDK detects the imminent navigation and automatically switches to navigator.sendBeacon() to guarantee delivery.

Why Pixel Helper does not show it

Pixel Helper instruments fbq() calls that happen during a normal page load. Events dispatched during page unload — or whose request is handed off to sendBeacon() — are outside the window Pixel Helper monitors.

What you see in DevTools

Event type Network tab response
Normal page events (AddToCart, ViewContent…) 1×1 GIF preview, status 200
Redirect-triggered events (CompleteRegistration) Failed to load response data

The Failed to load response data message is expected: sendBeacon() is fire-and-forget — the browser sends the request but does not expose the response body to DevTools.

How to verify the event was actually received

Since Pixel Helper and DevTools are unreliable for redirect-triggered events, use the Meta Events Manager instead:

  1. Open Meta Events Manager.
  2. Select your pixel.
  3. Go to Test Events (if using the test event code) or the Overview tab.
  4. Trigger the registration flow and wait a few seconds.
  5. The CompleteRegistration event should appear, typically attributed to the Conversions API channel (server-side) and possibly also the Browser channel (pixel via sendBeacon()).

CA is the authoritative channel

Because the Conversions API event is sent server-side — before any browser redirect occurs — it is always the reliable channel for redirect-triggered events. The browser pixel fires as a best-effort complement and is used for deduplication only. If both channels fire with the same event_id, Facebook deduplicates them automatically.