AdEspresso and Facebook both report the number of clicks on ad links that brought users to external websites. However, they use different metrics with different definitions to report these clicks.
Facebook reports ‘link clicks’ which include direct clicks on your ads that take people to your website. However, Facebook's numbers are usually higher because the 'link clicks' metric also includes visits to your website during what's called a 'view attribution window'.
The view attribution window is a period of days after an ad is seen, during which any website visits are attributed to the ad as a click. If a user views your ad, doesn't click on it right away, but visits your website later during the window, it will count as a click. They might click on the same link somewhere else, or visit your website anyway. So Facebook's clicks count also reports visits to your website that don't come directly from clicking on your ads.
AdEspresso reports the metric ‘inline link clicks’, which counts only those clicks on your ads that took users directly to your website. This metric doesn't have view attributions, is more reliable for reporting, and is easier to match with Google Analytics data.