Today, I was alerted that a custom FB audience list I created has reached 1000 people, so I can now use it. This list is comprised of visitors to a certain landing page which I advertise on Facebook exclusively. In the last month, there has been no other traffic to this page aside from Facebook. Red flag #1: Facebook reports there were 621 website clicks on my ad campaign. Red flag #2: Google Analytics reports about 450 visitors (including repeat visitors) over the same period to that landing page. If my custom audience here is built only from visitors to this page, how could that FB audience now be at 1000 if there were only 450 visits to that page? And meanwhile, FB reports (and has charged me) for 621 website clicks when total page visitors was only 450. I am confidence in my tracking, pixel and analytics is set up properly. Thoughts?
I am not a coder, so literally have no idea how the Facebook pixel works and what triggers a page view. But I suspect it might be spam engagement on Facebook's side. People just click and before your page is even loaded, they already leave. Maybe Facebook registers it as a "Page View" on their site, but because you page didn't load, GA couldn't be triggered. It is just a suspicion, I hope some other people can give you more insights.