“One of my invoices to my customer is wrong. What should I do?”
In cases like this the easiest solution is to reverse the invoice using a credit note, and then issue a completely new invoice (and hopefully get it absolutely right). A credit note is basically a negative invoice. It should replicate the incorrect invoice in every respect, except that the heading is “Credit Note” and not “Invoice” and all the figures should be preceded by a minus sign. The date on the Credit Note is normally the date you prepared it, unless there are compelling reasons to use a different date.
Let’s say that this is the incorrect invoice . . .
Use whatever the next number is (in your normal invoice number sequence) for the credit note. If your software forces you to use a different number sequence for credit notes, then we will live with that! We prefer a single number sequence if at all possible.
When your bookkeeping is done, and when your customer does their bookkeeping, these two documents will cancel each other out.
Then use the next number in your normal invoice number sequence for the new invoice.
Make your corrections like this every time and then you, your customer and your accountant will always know exactly what is going on. Thanks!