Why my custom purchase conversion only track 10% of my real purchases ?
Custom conversion set up on a shopify store with:
content_ids- on omega facebook pixel with facebook ads API
- ads use utms
My campaign / pixel tracked 14 sale on the product but the custom conversion only tracked 1…
Thanks in advance
The short answer is:
Your custom conversion is likely failing because it relies on the browser-side pixel and strict URL conditions which are easily broken by modern browser privacy features, ad-blockers, and complex checkout flows like PayPal, which often bypass the standard Shopify thank-you page.
To fix this, you should switch your reporting and optimization to the standard Purchase event that is sent via the Conversions API (CAPI) using a robust setup like Shopify API + Google Tag Manager + Stape, which guarantees much higher accuracy and better data quality.
The long answer is:
The massive discrepancy you’re seeing is very common and primarily due to the inherent limitations of custom conversions, especially in the current privacy-first environment.
A custom conversion is essentially a rule you create in Ads Manager based on a pixel event and a specific URL pattern, like “only count a Purchase event if the URL contains thank_you_page and the content_ids parameter is present.”
If the user reloads the page, navigates away too quickly, or uses an express checkout like PayPal that doesn’t consistently redirect back to the standard thank-you URL, the custom conversion rule is never met and the purchase is not tracked, even though the base Purchase event might have fired.
The simple solution is to stop using the custom conversion for a specific product and instead optimize your ad set for the standard Purchase event while making sure you are also sending the product-specific data (like your content_ids) as parameters within that standard event.
The ultimate fix, however, is to move your tracking to a reliable server-side setup.
A combination of the Facebook Conversions API (CAPI) through Shopify’s data layer, routed via a server-side Google Tag Manager implementation and a tagging server hosting solution like Stape or Google Cloud Platform, is widely regarded as the most accurate and future-proof method.
This setup works because the purchase data is sent directly from your Shopify server to the Meta server, completely bypassing the browser, ad-blockers, and cookie restrictions that currently block up to 60% of events on the client side.
By using GTM as a server-side intermediary, you get full control over the data being sent, ensuring perfect deduplication between the pixel and CAPI events, achieving a high Event Match Quality score, and sending rich, accurate customer data like email and phone number to Meta’s system for better attribution and optimization, all for a very low cost as Stape and GTM are either free or have a minimal server cost.
This approach transitions your tracking accuracy from the unreliable 10% you’re seeing to the 90%+ range, giving you the clean data Meta needs to efficiently optimize your campaigns and ultimately drive more sales.
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