Within Sales orders, Promotion Codes can also be used. These are based on the Codes which have already been generated in the "Promotion Code Groups" page. 

Adding a code to an order is simple. From the Sales Order ribbon, select 'Related', then 'Order' and then 'Document Promotion' Codes. 

In the Promotion Code field, enter the Code you are using and then close the screen. The Document Promotion Codes FactBox now shows you have a code applicable for the Sales Order. The Code you entered then gets updated on the "Promotion Code Group" card to acknowledge it has been used. Then you follow the same method to apply the promotion by selecting 'Apply Promotion' from the ribbon.