Please know that, Not every FB ad Click is really a click to the website. FB counts Likes, Shares, Comments, Lead ad form visits as Link Clicks.
To troubleshoot this discrepancy, you have to add custom columns in Facebook ads account.
- Link Clicks: Not every link click is a click to the website. Since FB counts likes, shares and comments as link clicks. You will also find a column named unique link clicks.
- Outbound Clicks: This column shows the clicks that took the user off of Facebook. The clicks that made users leave Facebook or its properties and visit the ads landing page. You will also find a column named unique outbound clicks.
Note: The outbound clicks does not necessarily mean the users visited the website so that Google analytics can capture it. There may be some discrepancy here as well.
Say, the user clicks on the FB ad and get to landing page, but even before the landing page (where GA code is present) loads he leaves the site, or your site is taking forever to load so analytics can capture the page view.
- Landing Page Views: This column shows the number of users that actually visited the site and the site was fully loaded and all the Tags were fired. (This is available only after you implement FB pixel on the site). You will also find a column named Unique Landing Page views.
So always check these 3 columns together when you are analyzing the performance of FB ads using Google Analytics data.
Since I am writing about this FB and GA discrepancy, it is important to know that FB takes 100% credit for conversion that happen on the website after an ad click within the default 28 day click attribution window.
So if a user likes the ad which is counted as a link click, then goes on to convert on the website within the next 28 days regardless of whichever marketing channel that brought the user, FB will record it as a conversion.
So if you have a multi-channel marketing, it is always recommend to decrease the default FB attribution window, so that FB does not take credit for a conversion that was heavily influenced and completed by other marketing channel.
Note: Facebook conversions data changes because of its default attribution model. If you check the conversion data on day 1, and then u check the conversion data for day 1 on day 20th, you will notice the change in the conversion data, since FB will attribute all conversions that happen on the website after day 1 until day 27th to the Day 1 Ad click.