Welcome to the Community, @lena21.

You can refund your customer's checking account by signing in to QuickBooks Payments and then reverse the transaction from the Processing Tools drop-down. There you can search for the transaction and select the sale you want to refund.

Let me show you how:

1. Sign in to your QuickBooks Payments account.
2. From the Processing Tools drop-down, select Reverse a Transaction.
3. Fill out the necessary fields and select Search.
4. Select the transaction(s) you want to refund, then Submit.

However, if you aren't subscribed to QuickBooks Payments, you can use refund receipts. Make sure you haven't created a credit memo because this would cause a double refund.

Here's how:

1. Select + New.
2. Select Refund receipt or Give refund.
3. Select the Customer ▼ dropdown, then select the customer you want to refund.
4. Select the Refund From ▼ drop-down, then select 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 select Save and close.

I'll add this video article as your guide in recording refunds based on various scenarios: Record a customer refund in QuickBooks Online. It includes how to refund a customer's overpayment.

If you wanted to learn more about alternative ways in processing refunds in QuickBooks Payments, here's your reference: Void or refund transactions in QuickBooks Payments.

Please let me know if you have more questions. I'll keep my notifications open. Have a good one!