Why this happens
The confusion mostly comes from Conversions API being positioned as "the fix for" cookie deprecation and ad-blocker loss, which reads to a lot of teams as "the replacement for" the Pixel rather than a second, independent path running alongside it. In Meta's own model, the Pixel and CAPI are two inputs into the same matching and attribution system - the Pixel captures fast, low-latency browser events with strong client-side context, while CAPI captures events your server is certain happened even when the browser did not cooperate.
Removing the Pixel does not make CAPI cover everything the Pixel did. Events that only ever existed as browser-side signals - a page view where no conversion followed, a client-side add-to-cart with no corresponding server record - simply stop being reported at all, and retargeting audiences built on that kind of browsing behavior lose their source entirely.
Fix it
- Confirm the Pixel base code is still installed and firing, checked via Meta Pixel Helper or Events Manager Test Events - some teams remove it during a CAPI migration on the mistaken belief it is now redundant.
- Confirm every event sent via CAPI has a corresponding client-side Pixel call for the same action, sharing an event_id per the dedup rules - running CAPI without the Pixel is not broken, exactly, but it forfeits the incremental recovery CAPI is meant to add, since there is no browser signal left to recover events against.
- Keep both running for standard events (PageView, ViewContent, AddToCart, InitiateCheckout, Purchase, Lead) where the Pixel has clean client-side visibility, and lean on CAPI-only sends for events that genuinely only exist server-side, such as a subscription renewal with no page load at all.
- Re-audit any retargeting or custom audience built from Pixel-only signals like "visited product page" - these depend on the Pixel continuing to fire, and a CAPI-only event stream cannot rebuild a browsing-based audience the same way.
How to verify it worked
- In Events Manager's Overview tab, check the source breakdown for core events (Purchase, Lead) - a healthy combined setup shows a mix of Browser, Server, and deduplicated-both sources; if Browser drops to zero for an event that should still have client-side coverage, the Pixel stopped firing somewhere.
- Run Meta Pixel Helper on the live site and confirm the base Pixel fires with no errors on page load, independent of whether CAPI is also configured.
- Compare total event volume before and after a CAPI rollout - volume should stay flat or rise as recovered events are added, and should never drop, when CAPI is added correctly alongside an unchanged Pixel.