I had a customer pay us with the wrong checking account. They asked for a refund check. I sent it, they cashed it. Now the refund check shows on my Aging Report. Help!

I'm here to help you record your customer's refund, @dntoto.

If a customer asks for a refund for an item or service, you can use the refund receipts feature. Make sure that you did not create a credit memo yet, to prevent a double refund.

Here's how:

1. Go to the + New button.
2. Select Refund receipt.
3. Choose the customer you want to refund in the Customer drop-down arrow. 
4. Select the Refund From drop-down, then pick the bank you deposited the payment for the invoice too.
5. Add all products or services the customer returned in the Product or service column.
6. Make sure to fill the quantity, rate, amount, tax, and other fields accordingly, then hit Save and close.

If you're going to refund a customer's overpayment or credit, please see this article for the detailed steps: Record a customer refund in QuickBooks Online. 

Also, just in case you want to record a refund received from your vendor, you may visit this page for the instructions: Enter a credit from a vendor. From here, you'll also learn how to apply the vendor credit toward any open or future bill. 

Please keep in touch if you need any more assistance with handling customer refunds or any QuickBooks-related issues. I've got your back. Have a good day and keep safe.