Cross-device reporting

• Third-party reporting platforms aren't able to measure cross-device conversions well due to cookie-based measurement. Because people are their real selves on Facebook, conversions can be captured more accurately in Facebook reports.
• Cross-device conversions from ads are common. Mobile conversions tend to be underreported by third-party platforms that measure with cookies.
  
  
  
  
  
• Facebook conversion tracking has the ability to track how your customers move between devices before they convert. Try compiling a cross-device report to see how mobile your audience is.

Clicks vs impressions

• If a person sees a Facebook ad for your product and doesn't click, but later browses your website and decides to purchase, Facebook is able to attribute this conversion to the Facebook ad the person saw. Third-party platforms are unable to capture such conversions.

Facebook doesn't only track last-click conversions

• Third-party platforms capture conversions that resulted from a direct referral. Even if you created a campaign using URL parameters to track the link used in your ad, third parties identify those “last-clicks,” or linear conversions, where the user clicked an ad and immediately converted.
  
  
  
  
  
• Facebook tracks conversions across devices and can also track non-linear conversions where a user clicked an ad, browsed, but left your site, then returned and converted. To track these conversions, Facebook uses a 24-hour window for views and a 28-day window for click through. Try changing the attribution window to view all your conversions.

Attribution windows

• Check that your conversion attribution windows match. By default, the Facebook conversion reports are set to a one-day after view or 28-day click window.

UTM Parameters (Referrer Links)

• Many third-party tracking providers use referrer URLs to credit conversions back to ads. These providers generally under-report Facebook conversions by about 40%. This is due to the fact that roughly 40% of people browse Facebook using HTTPS instead of HTTP and when someone clicks on an ad on Facebook and converts on a site, the referrer cannot be recorded since they left an HTTPS environment and entered an HTTP environment.
  
  
  
  
  
• In addition, if someone opens a new tab (for example, if you run to your meeting and go back to the website to purchase the product after work), the referrer URLs will no longer be there so the analytics tool will consider this sale a brand new person and not attribute it to Facebook.

Ad Blocker Software

• Your Facebook pixel may not fire if the user has an ad blocker implemented to the browser. This will cause undercounting conversions, hence, the number may be lower than your internal data.

Pixel implementation

1. Check whether your raw pixel fires match. If you're using the Facebook pixel, you can check how many times your specific standard events were triggered in your pixel dashboard.
2. If you're using conditional firing, expect a small discrepancy. Check that you're not using a combination of conditional/unconditional firing with your tags.
3. If your raw pixel fires match but there's a discrepancy in conversion values, check your currency, decimal places and other variables in your purchase event codes.
4. If Facebook is reporting more conversions than your other analytics tools, use the Pixel Helper tool to check for duplicate pixel fires, which can sometimes be caused by redirects.
5. If Facebook is reporting fewer conversions, this may have to do with the pixel piggybacking on existing tag managers. Check that this has been implemented correctly.