A Google Ads purchase conversion can look finished in the interface and still send the wrong value, count one order three times, or lose the ad click. This guide covers one conversion action: a website purchase. It sets the value, currency, transaction ID and enhanced conversions, then checks each part in a fixed order. Why Google Ads, GA4 and your shop still disagree after a correct setup is a separate question, covered in why Google Ads, Meta and GA4 report different conversions.
Create the purchase conversion action
Google's guide to setting up web conversions starts in Goals, then Summary, then Create conversion action. Pick the Purchase category and the Google tag as the data source. The same page offers a URL method for simple page loads, but it says the code method is required for dynamic values and transaction IDs. A purchase needs both, so use code or Google Tag Manager.
Two settings matter before any tag fires:
- Count. The help page on conversion counting options describes "Every" as the fit for sales, because every sale likely adds value. "One" suits leads.
- Primary or secondary. The setup guide warns that this choice is critical. Primary actions are used for bidding. Secondary actions are for observation only.
Send value, currency and a transaction ID
Each order should carry three things: its value, its currency and its own ID. Google's page on transaction-specific conversion values asks for the value as a number with a period as the decimal point, and the currency as an ISO 4217 code such as EUR. The says the ID must be unique for every order, up to 64 characters, and free of anything that identifies the customer. If two conversions share the same conversion action and transaction ID, Google Ads does not count the second one.
