"Open item" accounts are those where payments are applied to specific invoices. The alternative to this approach are "Balance Forward" accounts where the payment is simply applied to the outstanding account balance. The choice of which method is used is determined when you Set Up Account Preferences.
IF THIS IS A PAYMENT TO AN OPEN ITEM ACCOUNT . . .
1. After you have entered the payment amount on the Enter Payments window and pressed the key, do one of the following:
2. Either left-click on the key or left-click the button.
3. Either way, the Apply this Payment to? window will be displayed.
4. All of the open invoices for this account will be displayed in the grid with the oldest ones at the top of the list, like this:
5. If the selected invoice (the top one on the list) is the one that the payment will be applied to, left-click the button and then left-click the button.
6. If this is the only invoice to have the payment applied to, left-click the button.
7. If this is NOT the only invoice to have the payment applied to, select the next appropriate open invoice on the grid. Then left-click the button and left-click the button. Repeat this until all of the invoices to have the payment applied to have been selected. Then left-click the button.
8. This will return you to the Enter Payments window where you can enter the next payment in the batch.