Hi MelLindaB,
the usual process in customer order is that an advance invoice (or multiple ones) is issued and that invoice will be paid by the customer.  By paying (matching the payment you receiverd in your bank account against the adv. invoice) a CUstomerPaymentIAdvance CUPIA is created as a liabiltiy on the customers account. When the final invoice is issued the (all) payments in advance, registered under this specific customer order are deducted from the open amount of the final invoice. 
So to say a final is not “paid” by the advance invoice but by the payments received on the advance invoice.

An advance invoice might be only partially paid or payed with multiple payments or even is not paid. If no payment is received nothing can be deducted from the final invoice.

You can see on a customer order all connected invoices:

Or you can see on customer analysis the invoices and their relation to customer orders:
 

Hope this helps.

Regards

Hello @MelLindaB 

@Ralph Gericke is right. You are matching actually payment with customer invoice. However. IFS keeps the record of matching on ADVANCE_INV_REFERENCE view. There is no specific window to see this matching I believe.

I created a quick report for you. You can enhance the report based on your requirement

select identity, supplier_info_api.get_name(identity) name, invoice_api.get_invoice_no(company,invoice_id) cust_invoice_no,invoice_no adv_invoice_no,offset_amount,offset_dom_amount,currency from ADVANCE_INV_REFERENCE where party_type_db='CUSTOMER'

Hope this helps