Do you understand the causes of unapplied cash payment income in QuickBooks? If you use QuickBooks, you need to understand what unapplied cash income is. There are a few possible causes for the QuickBooks unapplied cash installment payment occurrence. One of them is the possibility that the installment was made without changing it or the nature of the sales. The ledger may contain a record of the product or service's sales. This could make it possible for the entire sum to transfer to an unutilized cash installment pay account without the actual transaction taking place.