Why is my Remarketing Pixel audience smaller than my SmartLink traffic?

If you add third party service tracking to your SmartLink, it is perfectly normal if your pixel traffic appears lower than your SmartLinks traffic. All of the clicks captured by your SmartLink may not be reflected in your remarketing pixel data for many reasons. Some of the common reasons for this can be found below: 

Repeat visitors
The same user may visit your SmartLink several times. These repeat visitors will only be included in your remarketing audience once.

Tracking blocked by ad blockers
Visitors to your SmartLink may be using ad blockers, which can prevent remarketing pixels from running. Those visitors cannot be included in your remarketing audience.

Facebook user not logged in
Facebook identifies visitors and adds them to your audience only if the visitor is currently logged into Facebook in the same browser. Otherwise, Facebook is not able to identify that user.