How to undo a single payment received for a batch of cust invoices but the payment is not listed in the reviewed bank transactions?

Hello there, @FCMarine.

Let me step in and assist you to undo your customer's payment.

It might be you recorded the customer's payment incorrectly. You can check the transactions in QuickBooks and your bank statement. If you received a single payment or in batch, you'll need to record it the same in your QuickBooks Online account.

You can undo the customer's payment by following these steps:

1. Go to the Sales tab.
2. Select All Sales.
3. Choose the payment you want to undo in the Type column.
4. Click the More button in the toolbar.
5. Select Delete.

For more detailed information on how to undo customer's payment, you can refer to this link: Undo the Receive Payment of an invoice.

You may use this article that helps you on how to receive and categorize invoice payment: Record invoice payments in QuickBooks Online.

If you have additional questions, feel free to leave a message in the comment section. I'll be happier to help. Keep safe, and have a great day.