Facebook credits (or attributes) an action to your ad if someone viewed or clicked your ad and then took a desired action (ex: purchased a product on a website) within a specified number of days. The number of days between when a person viewed or clicked your ad and then subsequently took an action is called an attribution window.
By default, the attribution window is set to 1-day view and 28-day click on Facebook, which means you see attributed actions that happened 1 day after someone viewed your ad and 28 days after someone clicked your ad. You can change this default on Facebook, or you can break down your data to show and compare both view-through and click-though attribution on Adphorus reporting screen.
You can select your look back period by clicking the Attribution Window dropdown menu. You can also select to include default attribution window and compare your look back period to the default period.