Shopify Sales Not Matching Google Ads Conversions

First, which direction is the gap?

Why Google Ads shows more than Shopify

• Two primary purchase actions. The Google & YouTube channel creates its own purchase action. If a GTM tag, an app or old checkout code also sends purchases — and both are set to primary — every order counts twice. In Google Ads, go to Goals → Conversions and check which purchase actions are primary.
• GA4 import plus a Google Ads tag, both primary, counting the same order.
• Thank-you page reloads without transaction-ID deduplication.
• "Every" counting set on a purchase action instead of "one" per click, in setups where it should not be.

Fix: keep one primary purchase action, set the others to secondary or remove them, and make sure the transaction ID is sent.

Why Google Ads shows fewer than Shopify

Some of this is correct and should not be "fixed":

• Other channels. Google Ads only counts orders that followed an ad click (and, depending on settings, some views). Orders from email, organic and direct are not its to claim.
• Attribution windows. A purchase 45 days after the click falls outside a 30-day window.
• Consent and blockers. Declined cookies and ad blockers stop the tag. Consent mode and enhanced conversions recover part of this through modelling and hashed first-party data.
• Date of conversion. Google Ads reports conversions against the date of the click, Shopify against the date of the order, so daily totals will differ even when nothing is wrong.

And some of it is a bug:

• Checkout changes. Shopify moved checkout tracking to customer events and pixels; stores that relied on old additional scripts on the order status page lost tracking without noticing.
• Conversion action set to secondary after an import, so conversions are recorded but not shown in the main column or used for bidding.
• Tag Assistant shows nothing on the thank-you page.

How to diagnose it in 20 minutes

1. Pick three recent days. Write down Shopify orders that came from Google (UTM or referrer) for each.
2. In Google Ads, segment conversions by conversion action and by day of conversion where available.
3. Take five order numbers and look for them in GA4 or your tag's debug output. Missing IDs point to consent, blockers or a broken tag. Duplicated IDs point to two tags. Wrong values point to tax, shipping or currency.
4. Check Goals → Conversions for every purchase action: status, primary/secondary, count setting, value source.
5. Place a test order with Tag Assistant open.

Why this matters more than a reporting gap

If Google Ads only shows a reporting difference in a dashboard, it costs you nothing. If Smart Bidding or Performance Max is learning from the wrong numbers, it costs you money every day: double-counted purchases make targets look easy and bids rise; missing purchases make good campaigns look bad and budgets fall.

For the GA4 side of the same problem, see why GA4 and Shopify report different revenue. If you would rather have it fixed, that is the first thing a Google Ads audit checks.