A credit note is issued by the seller or supplier of goods/ services if they raised an invoice charging the customer more than the actual amount. After a credit note is issued, the customer may not need to pay the full amount mentioned in the invoice. It is primarily a corrigendum for any mistakes in billing made by the seller.
On the other hand, a GST invoice is raised by the supplier for a successful transaction of goods or services. The recipient of the service or goods shall pay the entire amount, if the amount is right.