Invoice created but not completed, and not delivered to customer. What now?

I had started creating an invoice. It was not yet completed, so it had not been sent to the customer. I did not know that an invoice nr. had already been created for it and saved in draft. So I just started creating a new one.

Now there is a second line for this customer in my invoices summary. So one line with an unfinished and therefore not sent invoice. And then a second line with the finished invoice, which has already been sent to the customer and has since been paid.What should I do with the first, incorrect invoice? Just delete it? Or create a credit note?