Short answer: conversion tracking works when you first decide which actions count, which of them steer bidding and what they are worth. Then you measure them one way, on all platforms at once, and compare the result with the backend. Most mistakes are double counting, measuring the click instead of the result, and missing values.
By the TrackLead team. Technically reviewed by Pieter. Updated: November 2026.
What a conversion is
A conversion is an action on your site that has value: a purchase, a submitted form, a booked call. Each platform names it differently. In GA4 you mark an event as a key event, in Google Ads you create a conversion action, Meta uses standard events such as Purchase or Lead, and LinkedIn has conversions.
Before setting anything up, write down for each client which actions exist, what they are worth and which platform should optimise on them.
Decide what is primary
Not every action belongs in bidding. In Google Ads only a primary conversion action steers bidding; secondary actions show in the All conversions column. Meta and LinkedIn optimise a campaign on one chosen event.
Primary: the action that is revenue or a qualified lead, such as a purchase or a quote request.
Secondary: steps along the way, such as a download, a click on the phone number or starting checkout.
Value: give every primary conversion a value and currency, leads included. Without a value a platform can’t optimise on what it brings in.
Where you measure: browser, server or backend
Browser: a tag or pixel fires on the site, usually through Google Tag Manager. Quick to set up, but sensitive to consent, ad blockers and Safari’s cookie limits.
Server: the conversion goes to the platform through a server, with the Meta or LinkedIn Conversions API or with server-side tagging. Meta recommends using the Pixel and the Conversions API together.
Backend: the conversion comes from the store or the CRM, such as a closed deal. You send it back with an offline import or enhanced conversions for leads.
Most agencies start in the browser and add the server or backend once the client steers on conversion data. More on that choice in the difference between client-side and server-side tracking.
The five mistakes we see most
Double counting. A purchase arrives twice, for example through a plugin and through GTM. Give every purchase a
transaction_idin GA4 and use the sameevent_idin the Meta Pixel and Conversions API.Measuring the click instead of the result. A click on the submit button is not a submitted form. Measure the confirmation: the thank-you page or the event after a successful submission.
No value or currency. Revenue shows as zero and Smart Bidding or Meta can’t optimise on value.
Consent not passed on correctly. Without the right signals Google measures nothing after a decline and doesn’t model either. See Consent Mode v2 in GTM.
Wrong counting. In Google Ads you usually count one conversion per click (One) for leads and every conversion (Every) for purchases. Swap them and the numbers are off.
If Google Ads shows clicks but no conversions, go through the seven causes in Google Ads.
How to set it up
Make a measurement plan: for each action the name, where it happens, the value and whether it is primary or secondary.
Define the data layer: have the site push an event with value, currency and a unique ID to the dataLayer for every conversion.
Build the tags in GTM: GA4, Google Ads (with the Conversion Linker), Meta and LinkedIn, all on the same event.
Set up consent before you publish.
Test in Preview and in each platform’s debug tool, and only then mark actions as primary.
Compare with the backend after a week: same period, same definition of a conversion.
With TrackLead you set up the implementation in your client’s own GTM, on the host you already use, with monitoring included. Take a look at tracklead.eu.
Frequently asked questions
What is the difference between a conversion and a key event?
It is the same idea under another name. In GA4 a marked action has been called a key event since 2024; in Google Ads, Meta and LinkedIn it is a conversion or conversion action.
How many conversions should I track?
One or two primary conversions per account: the actions that really bring revenue or leads. Track everything below that as secondary, so it is visible but doesn’t steer bidding.
Why do Google Ads, GA4 and Meta show different numbers?
They use different conversion windows, attribution models and dates (click or conversion). Differences are normal. Compare each platform with itself over time and with the backend.
Do I need server-side tracking for conversion tracking?
No, it starts in the browser. Server-side helps when conversions are lost to cookie restrictions or when you want to send offline conversions back from the CRM.