This page is only available when you enable PrestaShop's B2B features. To do that, go to the "Customer Settings" page, and choose "Yes" for the "Enable B2B mode" option.
This page displays the outstanding report for some of your customers, meaning the amount of money you are allowing them to buy your products before they have to actually pay you.
When the B2B mode is enabled (Shop Parameters > Customers Setting page), three fields are added to the customer creation form:
You should fill these fields for all professional customers.
Once a customer with outstanding allowance buys from your shop, it appears in the Customers > Outstanding page. This enables you to get an overview of your current outstanding invoices.