The credit note serves to correct or refund an already issued invoice, without modifying it.
Key takeaways 
A credit note is created from an invoice (not a draft)
Automatic number AV-YYYY-NNNN
It reduces the paid amount of the invoice
PDF generated and sent to the client
Create a credit noteFrom an invoice, create a credit note by indicating the line items concerned and the reason. The credit note receives its number (AV-YYYY-NNNN) and automatically adjusts the paid amount of the invoice.
Refund (partial or total cancellation)
Correct a billing error
Adjust an amount
On which invoice can I make a credit note? On an already issued invoice (not a draft).
Is the credit note sent to the client? Yes, with its PDF.
Why a credit note rather than modifying the invoice? For compliance: an issued invoice cannot be modified, it is corrected with a credit note.
How do I refund the client? The refund must be carried out by your own means
