Set Up a Sales Discount Account Default

From the Maintain menu, select Default Information, and choose Customers. Sage 50 displays the Customer Defaults window.
On the Payment Terms tab, enter or select the discount G/L account. To display a list of existing accounts, select the Lookup button. To add a new account, double-click the field, which displays the Maintain Chart of Accounts window.

Typically, a "Sales Discount" income account is used.
Select OK to save your default setting.