If you are trying to modify, correct, or delete an e-invoice that has already been validated by LHDN and are seeing this error message, direct amendments are not possible. Only invoices with a 'Review' status can be edited or deleted in the E-Invoicing Outgoing Dashboard. To correct a validated invoice, you will need to cancel it via the LHDN portal (within 72 hours of validation) or issue a credit note.
Just so you know, only an eInvoice with the status 'Review' can be edited or deleted on the E-Invoicing Outgoing Dashboard. No amendments can be made to eInvoices with the status 'Validated'.