With Lemon.js, when subscribing to Lemon events, a Checkout.Success event is received when an overlay has successfully completed an order. This contains information about the order, but crucially, it only contains information about the license identity, but not the license itself. ( The license ID is contained within the links key of the order object included in the event payload ).
If you are creating an in-app purchase experience using overlays, it would be useful to be able to intercept this event and inform the containing app as to the new license key, so that the user does not have to copy it or retrieve the data from their email. Reducing this friction would improve the sales experience of the user and the app.