If you get any mistake in any of your existing invoice, you can send a credit note to your client. The credit note will reverse the amount of the invoice.

To create the credit note, please go the the invoice details view. 

• Click on the Create credit note menu form the Actions dropdown. 
• A confirmation modal will appear there.
• You can create credit note from there.  

The main invoice's status will be changed to Credited and a new credit note will be created. You can see the credit note on the invoices list view.