How do I reverse a received payment?

Thanks for posting here, @jmfreebairns. I'm here to ensure you'll receive the payment to the correct invoice in QuickBooks Online (QBO).

You can reverse the payment applied to the wrong invoice by editing the transaction and receiving it against the correct one. Let me guide you how:

1. Open your QBO account and go to the Sales menu.
2. Next, click the Customer option.
3. From there, find the customer where the paid invoice (wrong invoice) is located.
4. Click the name to open the Transaction List.
5. Look for the payment transaction you've entered and click it to open.
6. You'll see the Receive Payment screen. From there, edit the details of the payment.
7. Select the correct name of the customer if the correct invoice is from the different one. If the same customer, check the box beside the correct invoice to apply for the payment against it.
8. Choose Yes and click Save and close. 

Once done, you can go back to the Sales menu and see if the payment was successfully received against the correct invoice.

I've also added this article for another option in correcting payments received against the wrong invoice: How to fix a payment applied to the wrong customer invoice. 

You might also want to run the Accounts Receivable ageing summary report to have a list of your customers’ outstanding balances. This will show you how much are still due and how long they're past due.  

I got your back if you have any other concerns about reversing payments applied to a wrong invoice. Feel free to post again here. I'd be glad to help you further. Have a good one.