How to Track Facebook Ad Conversions Across Main Domain to Subdomain

Ads not tracking conversions on subdomain.

Help Please, I am pretty sure my recent fakebook ad campaign is successfully getting me sales.

My setup for the Meta Pixel is so…

Meta Pixel on main website.

The same Meta Pixel is on the subdomain (this is where a purchase happens)

I have a purchase event set up on the confirmation screen.

Facebook is accurately tracking Purchases and Page Views.

The problem is my ads I run with this pixel always show 0 Purchases although I have had multiple.

Is the tracking not working going between the subdomains? Are they not able to track that the source was from the Facebook ad?

Not too sure how the tracking for this sort of thing should be done and or If it is the correct way I have it setup using the same pixel for the main website/landing page then the subdomain the sale happens on.

Any information on this, tips or insights on why fakebook wont be tracking this?

The short answer is:

The long answer is:

The good news is that your setup, using the same Meta Pixel ID on both your main domain and the subdomain for the checkout and confirmation screen, is the correct way to handle cross-subdomain tracking.

The pixel automatically manages user identity across subdomains of the same root domain.

The fact that the Purchase event is accurately showing up in your Meta Events Manager confirms that the pixel itself is installed and firing properly.

This means the problem is almost certainly not an issue with the pixel’s code or its ability to track between the domains.

The common culprit when the pixel is firing in Events Manager but the ads show zero purchases is a misconfiguration at the campaign level.

You need to verify that in the ad set settings of your ad campaign, under the “Conversion Event” section, you have explicitly selected the correct pixel and the Purchase standard event for optimization and reporting.

If you select the wrong pixel, or if you select an incorrect event like Lead instead of Purchase, the ad reporting will show zero conversions even if sales are happening.

If you have checked and re-checked your ad set configuration and the numbers are still significantly different, then the issue is a loss of data signal due to modern browser privacy restrictions and ad blockers.

Safari’s Intelligent Tracking Prevention (ITP) and similar features in other browsers aggressively limit the lifespan of the third-party cookies that the Meta Pixel relies on to link a user back to the originating ad click.

This is where server-side tracking, known as the Facebook Conversions API (CAPI), comes in as the essential modern solution.

Instead of relying on the browser (client-side) to send the conversion data, CAPI sends it directly from your web server to Meta’s server.

To implement this without extensive custom coding, the combination of the Facebook Conversions API + Google Tag Manager’s Server-Side Tagging + a dedicated tagging server host like Stape or Google Cloud Platform is highly recommended.

GTM allows you to manage both your pixel and CAPI events from one dashboard, while a service like Stape provides a very easy and cheap hosting solution for your GTM server container.

For instance, Stape offers a free tier or very low-cost plans that are significantly cheaper and simpler to maintain than setting up a full server on Google Cloud Platform (GCP).

By running your server-side GTM container on a service like Stape and mapping it to your own first-party subdomain (e.g., data.yourwebsite.com), the tracking is viewed by browsers as first-party data, which is far less likely to be blocked.

This setup ensures you capture nearly all sales, provide Meta with a much higher quality signal, and improve your Event Match Quality, all of which directly lead to better ad optimization and more accurate reporting.

This is the single most effective way to eliminate the discrepancy you are currently experiencing.

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