I am working on a project where I and the client agreed on a fixed amount project and some extra buffer amount for any extra work. And I suppose to get paid after the completion of the project.
I completed the project with a 1-day delay. The client was ok with that because it was submitted on weekend. I submitted an Invoice for the complete payment on Monday. I was busy with some other project so didn't bother about the payment.
On Wednesday (2 days after sending the invoice) the client told me to cancel the previous invoice and send one more Invoice with the extra buffer amount. In the old Invoice, the buffer amount was not added.
Now I am confused about how to cancel the old Invoice and send a new one? I submitted the Invoice through email.