If you allow customers to pay on account, you can find these accounts under the heading 'Finances > invoices'.

Go to 'Finances > invoices'.
To select all the invoices in a time period you can specify a time period under 'All items'.
Select one of the orders in question. Via the 'Reports' menu you can print or download orders - to send as an attachment to the invoice.
Choose a detailed overview: List current selection - that shows all of the customer orders detailed separately. Or choose accumulate current selection that shows all of the customer orders combined.
To clean up the list you can use 'procedures'. To indicate that these open items will be processed externally, click "ok" and the list is cleaned up and you can continue with the next invoice.

Under 'invoices debtors' you will find customers that are part of a debtor or organisation. Here you have the option to click on one of the accounts of the organisation.
By choosing a List current selection at 'Reports', all the orders of this organisation will be shown and can be sent as an attachment with the invoice. Here you can see all orders separately and in the upper right corner you can choose to download them.
To clean up the list, go to 'Procedures' where you can indicate that these open items will be handled externally. Press "ok" and the list is cleaned up. You can continue with the next debtor.

Invoices