When Invoice Ninja is connected (Settings → Payments → InvoiceNinja), PostalPoint records every sale as an invoice and every postage purchase as an expense. By default, sales go to a single "holding" client, or to an existing client whose ID you enter in the settings.
To track a regular customer's purchases in their own Invoice Ninja account, find their PostalPoint account ID on the Point of Sale page in the Customer card. Then enter it in the ID Number field of that client in Invoice Ninja. All future sales to that customer will go to their Invoice Ninja account, where they can view invoices and pay online.
This is ideal for business customers you bill monthly instead of at the register.
Automatic Invoice Ninja Client Creation
Under Settings → Payments → Invoice Ninja, turn on the Create client records switch. With this turned on, any time there's no Invoice Ninja client with a PostalPoint customer's ID number, and PostalPoint has enough customer data to create an Invoice Ninja client, the client record will be automatically created and linked for you.