Full Answer

Meta's Event Match Quality score measures how well the customer identifiers you send match real Facebook and Instagram profiles. The score runs from zero to ten, and it directly affects how many of your conversions Meta can attribute to your campaigns. A low EMQ means Meta cannot match your purchase events to the users who saw your ads, so the algorithm loses signal, bidding degrades, and reported ROAS drops — not because fewer people are buying, but because Meta cannot see who bought.

The most impactful parameters are hashed email and hashed phone number, because these are the identifiers Meta matches with highest confidence. Adding an external ID — a persistent first-party cookie or WooCommerce customer ID — provides a fallback match path when email or phone are missing. Every additional parameter you send increases the probability of a successful match, but email alone typically moves the score from the five-to-six range into the eight-to-nine range.

The reason Pixel-only setups score poorly is structural. WooCommerce checkout flows often redirect through PayPal, Stripe, or Klarna before returning to the thank-you page. By the time the Pixel fires, the session context that carried the customer's identity may be broken. Server-side implementations read the customer data directly from the WooCommerce order object at the moment payment completes — no browser dependency, no redirect risk. For a deeper look at how Meta's tracking layers stack, the distinction between Pixel, CAPI, CAPI Gateway, and Signals Gateway matters here.