As Facebook and Apple are combating the user's privacy war, all tracking events related to Pixel have been messed up. Some of the event data is probably missing and blocked from IOS devices, which counts for 26.46% of all mobile devices and 42.24% of all operating systems (1). That is a huge gap in the data analysis if advertisers want to run marketing campaigns and optimize later. So Facebook has developed the Conversion API for tracking conversion more precisely on Apple devices. It enables the servers side of your websites/e-commerce stores to send the data for tracking.