How the relay works

Every event takes the same path. Knowing it makes most questions, and most problems, easy to answer.

1. The browser sends the event to the relay#

The tracker script on your site collects the event: its name, the page address, the referring site and any details you passed, like an email address from a form. It queues events for a few seconds and posts them to your website's tracking endpoint on Pixel Relay. Nothing goes to Meta from the browser.

2. The relay checks who sent it#

• The API key in the address must belong to an active website. A paused website refuses events.
• The page must be on one of the website's allowed domains (or a subdomain of one). Requests from anywhere else are refused. See Allowed domains.
• The client account must be under its monthly event limit, if it has one.
• One visitor may only send so many requests a minute, the website's rate limit.

3. The relay cleans the event#

• The page address loses its query string and fragment, so ?email=... or #booking never reach Meta.
• Blocked terms in the address and in content names are replaced with page, so /ivf-consultation becomes /page-consultation.
• Email, phone, first and last name and your own user ID are normalised and hashed with SHA-256. Any other personal field is dropped.
• The site's own domain is swapped for the relay's when Hide the site's domain from Meta is on.
• The visitor's IP address is added only when Send visitor IP and browser to Meta is on.

The full list is in What the relay removes.

4. The relay names the event#

Your event name is matched against the website's event mappings. schedule_appointment can become Lead, purchase becomes Purchase. A name with no mapping is sent as a meaningless code like evt_a1b2c3d4, so an unexpected name never tells Meta anything.

5. Meta receives it, and the relay records the result#

The relay posts the event to Meta's Conversions API with the website's pixel and access token. It then logs the sanitised event with whether Meta accepted it. That log is what you see in analytics, and what the Failed to deliver page is built from.