Hi
To book expenses at SO level, the SO must be a Cost Object.. Usually it is not.. It is created as Cost Object in a specific MTO case, where you expect significant costs to be incurred to sell the product.
Eg: A Car Seller incurs many expenses while selling the car like Seat Cover, Music System, Blue Tooth, etc. All these expenses cant be envisaged while the Product is manufactured, as it depends on the Customer choice. Hence, you create SO as cost object in this case to collect all these expenses
If your case is like this, where you incur expenses at the level of sales order, define your SO as CO object by assigning a Requiremetn Class that has Account Assignment Category E
If you just want to charge Sales Overhead to Sales Unit, then create a CC for Sales Unit, assign the Sales Unit's PC in this CC and book expenses in this CC
Ajay M