Doug wants to be able to take orders from certain regular customers and generate an invoice for them, and mark that payment is due in four weeks time. This can be done with the invoice module.
The invoice module allows us to create and manage invoices for our customers, which can then be posted to them. The module is not enabled by default, so we need to go into the Modules section under Site building and enable the Invoice module.
The module also provides us with some new settings within the Invoices section under E-Commerce configuration.