Due to VAT certification, an invoice that has already been sent cannot be modified directly. To correct the mistake, you will have to follow this procedure:

1. In the Documents page, select the invoice you wanted to modify, create a credit note based on it through the "Other actions" button, and send the credit note. This "cancels" this specific invoice:



2. Go back to the Documents list, find the invoice again, and click on "Use as draft" to create a new invoice based on this old one. Add new details and make whatever changes you want to make, and then send it: