We constantly track the UTM parameters, and when they are clicked, we can link them to a sale and, therefore, report an attribution. We track when the customer arrives in the store via the UTM link.
Below, you find some reasons why sales still get attributed to your campaigns after they stopped running. (This is mainly applicable to large accounts since the likelihood is rising with increasing ad spend)
Someone saved the ad in Facebook
Someone saved a link with UTMs in their browser
Comments under ads contribute to clicking on it
Someone sent the ad via a Messenger and it was opened later
Someone clicks on the ad while it is still active, but buys after a few days