A Sales invoice is the means by which you charge a customer for goods or services they have received through a Dispatch, or for goods or services they have returned through a Dispatch return. A Sales invoice can also be used to charge for Non stock items that are not related to a specific Dispatch for a Customer, or to give credits that are not related to a specific Dispatch return.
A Sales invoice that is not generated for a Dispatch or a Dispatch return can only contain non-stock items: it cannot perform any Stock transactions for stock items. To perform stock transactions on a customer invoice, you must use the POS Invoice facility. POS Invoices can be managed through the same interface and regular Sales invoices, but will show the word P.O.S. at the top left of the form.