Different Platforms. Different Conversion Attribution.
From a big picture perspective, different platforms count attribution differently. Understand that when you’re inside of the Facebook platform, credit is attributed differently than when you’re in, let’s say, Google Analytics.
Google Analytics counts attribution to be the very last thing that somebody does overall. So, considering all your different types of marketing such as organic, ads, some referral traffic, etc. it’s going to count as the very last thing that a person does. As a result, fair credit is not given to the other actions people may take before taking an action that results in a conversion.
For example, someone sees a Facebook ad but then ends up doing an organic search later. The last thing they did was an organic search so organic search gets the credit or attribution, not Facebook.
Consequently, always measure how your Facebook ads are doing inside of the Facebook platform.