What is the Conversions API (CAPI), in plain words?

The Conversions API, or CAPI, is a way for your own server to tell Meta that something happened, such as a lead or a purchase, instead of leaving that job to a script in the visitor's browser. It sends the same kind of event the Meta pixel sends, just from your side of the fence.

That matters because browsers lose events. Ad blockers, privacy settings and short cookie lifetimes all get in the way of a pixel, while a message from a server does not care about any of that.

Here is the picture I use. The pixel is a courier standing in the visitor's browser, shouting to Meta that a sale just happened. If the visitor has a blocker, the courier never gets through. CAPI is a phone call from your back office. Nobody can stop it in the browser, because it never runs there.

An example, and it is made up: a small shop called Northside Candles runs Meta ads. On a Tuesday, 100 people buy. The pixel reports 71, because 29 buyers had blockers or a browser that cleared the ad click too early. The shop's server knows about all 100 orders. With CAPI, the server sends those orders to Meta, and Meta sees a much fuller picture of who is buying.

What does an event actually contain? At minimum, an event name such as Purchase, the time it happened, where it happened (usually a website), and some details that help Meta work out who the person was. Those details are usually a hashed email, a hashed phone number, and browser identifiers like the fbc and fbp values if you have them. Hashed means scrambled in a fixed way before it leaves your server, so Meta gets a scrambled version of the address and not the address itself. For purchases you also add a value and a currency.

Then there is event_id, which is a small label you attach so Meta can tell that the pixel and your server are describing the same moment. If both send the same event name and the same event_id, Meta keeps one and drops the other. Without it, you can count every sale twice.

The second thing to know is quality. Meta gives events a match quality score. The more real identifiers you send, the more of your events Meta can tie to an actual account, and the better its ad system learns. Sending an event with no email and no phone is technically valid and mostly useless.

Now the honest limits. CAPI does not create data you do not have. If your checkout never captures an email, no server can send one. It also does not make tracking legal on its own: you still need consent where the law asks for it. And it will not fix a broken offer, only a broken measurement.

Another limit that catches people out: Meta rejects events that are sent too long after they happened. Check the current documentation for the exact window, because it has changed before. Sending a batch of old sales weeks later is a common way to get silent rejections.

So who is CAPI for? Anyone paying for Meta ads who has a server, a shop platform or a tool in between that can send events. If you sell online, run lead forms, or close deals in a CRM after the ad click, it is worth having. If you get five leads a month and never optimise, it is probably not your first fix.

Are you starting from the pixel only, or do you already have some server events going out?