Facebook Ads Conversion Pixel DOES Work
Here's an example:
Campaign 1 going to page:

Campaign 2 going to same page:

And the earnings so far on this one:

So my conversions are 11 + 4 = 15 total.
But I'm showing I have 29! Why the difference? Why is Facebook showing me 15 and yet there's 29 sales?
Simple.
On Facebook, your posts get SHARED. When they do and someone buys from that share, they didn't click on the ad, they clicked on a shared post. So that means no conversion registers with the Facebook Ad interface!
Makes sense now, but I was getting annoyed with it before.
Hope that helps clear up any confusion.