The first screen shot that you have posted shows that all invoices, for the Customer account, are “Paid in Full”. The second screen shot shows that this Customer has a positive AR balance. A positive AR balance is a debit balance and this would suggest that there should be outstanding invoices that are awaiting for funds to be received from the customer.
Therefore, there must be some other debit transaction(s) that has(have) been coded directly to the Customer AR account without allocation to any invoice(s).
Possible transactions could be:
- Receipt from customer processed as a payment rather than a receipt.
- The Customer AR account debited in a journal transaction.
- A Credit Note transaction using a negative amount
There may be others. I have ruled out a debit starting balance as this can only be achieved by entering invoice details.