When debit note and credit note issue?

A debit note is a note indicating the amount owed by a person or company. It serves the same purpose as an invoice.

A credit note is a form or letter sent by a seller to a buyer stating that a certain amount has been credited to the buyers account. Also called a Credit Memo, and are issued when there is a mistake or return of merchandise.

The issuing of a credit note may be because of they were not given the correct discount, the item or purchase didn't meet the customers expectation and they returned it. Those are only a couple of example.