When a sales document has been posted we can also view the Promotions that were successfully used on it, a new action is added to the Navigate tab in the ribbon called Promotion Summary.
The Promotion Summary as displayed above shows a list of the promotions that have been used in the document.
When clicked, the Promotion Summary action will show the details behind the applied promotion(s). In the screen shot you can see the Promotion Code, Description and additional line that was added, in this example with a quantity of one at 100% discount.
The Promotion Summary as per above shows how the applied promotion is transferred from the non-posted document (e.g. a Sales Order) to the posted document (e.g. the Posted Sales Invoice), it shows you the Promotion number that was successfully applied and the benefit line that was applied or changed.