When you did this: "We updated the invoice in quickbooks."
You just changed your Financial History, your Sales, and if that is a tax year already reported, you just changed All of it. If that included changes to inventory items, you just affected inventory.
Here's what you should have done:
If the invoice is Paid and done, you make a Credit Memo (return/refund) dated now for what was Wrong. Your refund that, or are going to use it to apply to the New Invoice dated now for what was overlooked. If the invoice was not paid at all, a credit memo dated Now would be used to reverse everything on the invoice and you apply them to each other. Then, the New invoice dated now is, "Let's start from the beginning, and correctly."
Or the original invoice is not paid in full, and you list on a credit memo dated Now, what was wrong, to reverse those and end with a Value that is you Apply to the rest of the unpaid value.
In other words, what you want to be able to show the customer is the Credit Memo you should have made, how it affects the previous invoice is from the perspective of Value applied if that previous invoice was not already paid, if they get a Refund, and/or if there is a New Invoice to get your sale to them on track, all dated Now.
Not editing historic transactions.
Run your reporting to see what you affected. You can put it all back how it was, then make that credit memo and take the proper action moving forward, dated Now.
