Received a payment from an account but they changed their mind on amount of product so they want the difference back. When I try sending it the message says canceled

You can enter a refund to resolve the difference for paid invoices in QuickBooks Online (QBO), Kelsey. I'll provide more details below and walk you through the process to ensure seamless navigation.

Before we proceed, I'd like to know more about the canceled payment for a specific invoice. Did the payment go through before your customer canceled the payment, or did the payment not go through due to an error?

Depending on the situation, you can enter a credit memo before refunding a customer. By doing so, QuickBooks will return the items associated with the transaction to your inventory. Here are the steps:

1. Select + New and select Credit memo.
2. In the Customer field, select the appropriate customer.
3. Enter the Credit Memo Date, Amount, Tax, and Product/Service (This is the category, product, or service you’re getting a credit for). A reminder, if you choose an inventory item, QuickBooks will put it back into inventory. If the item is defective or if you don’t want it added back to inventory, you can make an inventory adjustment.
4. Click the Save and close button.

If you treat this situation wherein the customer overpaid the invoice, you can skip entering credit memo and proceed to make the refund. Explore Step 2 in this article for further guidelines: Record a customer refund in QuickBooks Online.

In addition, you'll want to run a report to review the sales and the status of your inventory in QBO. Feel free to visit this page for more details: Use reports to see your sales and inventory status in QuickBooks Online.

I'll be around if you require further assistance streamlining invoicing tasks or have any additional QuickBooks-related concerns, Kelsey. I encourage you to comment below so I can respond and provide the details you need. Keep safe.