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 counts visits to your website during a view attribution window.
If a user only views your ad, but doesn't click on it, if they later click on the same link somewhere else or visit your website anyway, that will be attributed to the 'link clicks' metric through view instead of click. What this means is that 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.