Joyce has a webshop with branded clothing. She just started and she ships the clothes from her warehouse. There, she also prepares the invoices for her customers.
Recently, Joyce made an invoice for a customer who ordered two T-shirts. She sends the invoice along with the T-shirts. Two days later, her customer emails that he has received the T-shirts in good order, but that there is an error on the invoice: the T-shirts delivered are Large but the invoice says Extra Large and they are slightly more expensive. The customer asks if he can get a new invoice.
Joyce thinks for a moment and decides to manually adjust the invoice; she changes the size of the shirts and she changes the price, which means that the VAT had to be adjusted too. She leaves the invoice date as well as the invoice number and mails the adjusted invoice to her customer.
You would think that Joyce has solved it nicely and in many cases it will go well, but was she wise to adjust the existing invoice? There are now two invoices with the same invoice number and date, but with different items, different prices and a different VAT amount.
No, I don’t think Joyce should have done that. The royal road would be to create a credit invoice from the original invoice and then create a new invoice with the correct items, prices and VAT. You simply continue to number, so there are three invoices for this customer. That seems superfluous, but this is the correct way.