Reasons for Variance in the Advertising Reports and the Business Reports
The Advertising Reports and the Business Reports show discrepancies in data due to sourcing differences from where they are retrieved.
Attributed purchases for advertising reports and Business reports will vary as Business report sales are based on the day of the sale, whereas advertising reports are reported based on the day the ad was clicked.
Customers can look at an ASIN, add it to their cart, but place the order at a different time in the future. Thus the page view is made on a different day than the sales. If the date for the page view isn't within the time range selected in the report, then it isn't included.
Due to these differences, the clicks recorded in the advertising reports on the ASINs are different from the page views captured in the Business reports. Therefore, Amazon always suggests you to view the Campaign manager/Advertising reports for data related to Advertisement and don't compare this data with the Business reports.
Also, the data will be different as the sales related to ads will be calculated differently compared to the organic sales that we see in business reports. You might be seeing the sales information in the business reports only for the advertised products. However, Campaign Manager shows the date for the products purchased after clicking on ads. This is the reason, you see a difference in sales number.