A credit note (or credit memo) is a commercial document issued by a Seller to a Buyer. The Seller usually issues a credit note for the same or lower amount than the invoice, and then repays the money to the Buyer or sets it off against a balance due from other transactions.

Please note that Tradeshift does not allow the total amount on credit notes to be negative. If the document is a credit note, it is implied that the total amount from it has to be credited to the Buyer's account.

Since invoices, depending on local regulation, are not to be edited after having been sent, the only way to make corrections is by sending a credit note against the invoice. 

Read this article to find out how to create a credit note.