Hi there, JudyC61.

Thank you for visiting the QuickBooks Community. I'll provide some details you'll be able to sort the error message you received. Then, ensure that you can write off transactions.

When choosing invoices to be paid on the Receive Payments screen and the total of all invoices exceeds the figure in the Payment amount field, you'll get the message that indicates "You cannot apply an amount greater than the total payments plus any existing credits when creating a payment in QuickBooks".

To start with and to fix the issue, I recommend applying a discount or credit to one or more invoices. 

Here's how:

1. Choose the invoice line without checking it (highlight the invoice by clicking the date or number field).
2. Select the Discount and Credits button. Then, to apply a discount:
   1. Click the Discount tab.(Optional) Change the amount of the discount.
   2. Note: QuickBooks calculates a suggested discount amount based on your payment terms with the customer and the payment date. You can enter any discount amount you choose; you don't have to use the suggested amount. However, the amount of the discount can't be higher than the original invoice.
   3. Enter the name of the expense account you use to track discounts. (Example: Discount Expense).
   4. Click Done to record the discount.
3. To apply for a credit:
   1. Click the Credits tab.
   2. Put a checkmark on the credit you want to apply.
   3. If you do not want to use the entire credit or if the credit amount is more than the customer balance, change the amount under the Amt to Use column.
   4. Click Done to record the credit.
4. Select the Save & Close button.

If the issue persists, you can change which invoices are selected to be paid. You can open this article to see the steps on how to perform the process and follow solution two: Warning: You cannot apply an amount greater than the total payments plus any existing credits.

Lastly, you may open this article to view different ways on how you can track customer transactions in QuickBooks Desktop: Get started with customer transaction workflows in QuickBooks Desktop.

Let me know if you still have questions or concerns about achieving a write-off in QuickBooks. I'll be around for you. Take care and have a good one.