Why won't QuickBooks let me edit an invoice already sent

Hello Havenhomeimprove, thanks for getting in touch about invoicing. We just need to ask a few questions based on what might stop you being able to edit an already sent invoice. Can we check what it is you are trying to edit? Have you recently filed VAT in QuickBooks for the period the invoice fits within? Are you on FRS for VAT? Do you have a close the books date set in QuickBooks? Thanks