Once an invoice has been issued, you can cancel it within 48 hours if necessary. However, if the invoice has already been delivered to the client and recorded by an accountant, the best approach is to void it by issuing a Credit Note for the full amount.
If you need to reduce the price or quantity of goods/services on an Invoice or Invoice-Receipt, and the invoice has already been issued and delivered, you must issue a Credit Note. For more details, see the article "What is a Credit Note?"
If you need to increase the amount due to the sale of additional goods or services, the simplest solution is to issue a new Invoice or Invoice-Receipt for those additional items.
If you need to increase the invoice amount due to a VAT rate adjustment (e.g., if a lower VAT rate was mistakenly applied), you would typically issue a Debit Note for the VAT difference. However, due to the complexity of this process, this functionality is not available in FIZ. Instead, you can simplify the correction by issuing a Credit Note for the total invoice amount and then issuing a new Invoice with the correct values.