If you send an invoice and then want to cancel it, you can, as long as it has not already been paid.
Go to My Dashboard and under "Project" select the project you are referring to. You can also click on the invoice sent under "Activity" to access the same project screen. From here, find the specific invoice you want to cancel and select Cancel Invoice.
If you’re sure this is the invoice you want to delete, select Yes on the following confirmation screen.