Problems Posting Payments to an Invoice

[Terry Morse]

GNUCash 2.6.3 on a Windows 7 64 bit laptop.

In reviewing my "client's" (actually a friend; I'm doing this for free) accounts to generate year-end tax reports for her customers, I added some charges to the beginning of a customer's invoice that are credited to the income account "Income: Sales." When I try to enter payments for the new entries (either before or after reposting the invoice) through the Process Payment dialogue box, there is no outstanding balance listed in the Documents field to which I can link the payment. Hence, I am not able to enter the payment. The "post to" account is Accounts Receivable and the transfer account is Orphan--USD.

What am I doing wrong here?

Thank you,
Terry