This is a deep dive into Meta’s Attribution Setting. Here are some notes…
WHAT IS THE ATTRIBUTION SETTINGAttribution is how Meta gives credit to an ad for a conversion. Your Attribution Setting determines how your ad will be delivered and the reporting attribution window. The default Attribution Setting is 7-day click and 1-day view, which means that anyone who converts within 7 days of clicking or 1 day of viewing your ad will be counted as a conversion. More?
This comes into play when using the Website conversion location (found when using the Sales, Leads, or Engagement objectivesWhen you create a campaign, one of the first things you'll do is select an objective. The campaign objective is your ultimate goal. Your selection will impact options, including optimization and delivery. Options include Awareness, Traffic, Engagement, Leads, App Promotion, and Sales. More). It utilizes your pixel and a conversion event.

By default, the Attribution Setting is 7-day click and 1-day view. An attributed conversion, in this case, is any conversion that happens within 7-days of clicking your ad or 1-day of viewing your ad (without clicking).

That also means two things:
1. Meta will optimize to show your ads to people most likely to convert within that window.
2. Your default reporting will be attributed conversionsA conversion is counted whenever a website visitor performs an action that fires a standard event, custom event, or custom conversion. Examples of conversions include purchases, leads, content views, add to cart, and registrations. More that happened within that window.
RECOMMENDED APPROACH TO ATTRIBUTION SETTING
You can change your Attribution Setting. In some cases, I recommend that you do.
1. If you’re running a Sales campaignThe campaign is the foundation of your Facebook ad. This is where you'll set an advertising objective, which defines what you want your ad to achieve. More, the default of 7-day click and 1-day view is typically best practice. If you’re running a video ad, also include 1-day Engaged View.
2. If you’re running a Leads campaign, you should usually change the Attribution Setting to 1-day click. There are potential exceptions when completing a form may still be a longer-term process. But if you’re offering something free in exchange for contact information, use 1-day click.
3. If you’re running an engagement campaign that optimizes for custom eventsConversion events tracked by the pixel, app SDK, or API that are outside of standard events. These tend to be created to fit the publisher's needs when a pre-defined standard event will not. More, you should almost always use 1-day click. Most custom events are things that someone will do repeatedly, especially based on engagement (time spent, scroll depth, watching videos, etc.). Meta will inflate your numbers by reaching people who go to your website anyway with 1-day view. Prevent that.