Comapring apples and oranges.<p>Facebook ad clicks are not the same thing as advertised website's uniques/visitors/hits/sessions/whatever. Especially if the latter is using external tracking that uses JS and tends to be blocked/opt-out by some.<p>Facebook clicks are really 'clicks', not 'unique people clicking', they are also not 'successfully redirected after click', maybe not even 'click successfully finished and not reverted by aborting'. It just means someone clicked or tapped on the thing used to advertise.<p>So yes, you get what you pay for, and in the case of Facebook it's their definition of a 'click' you are paying for.<p>By the way:
You get pretty close to their numbers when using a redirect script that loads in a few ms and just writes 'hits' to a database and then again redirects to you to your normal target website. Not 100%, but much better than using GA or any other external tracking on the target website.