Here's how to make a correction in FreeAgent that falls into a VAT locked period if you've already filed your VAT return online.
Editing invoices in a VAT locked period
Invoices can be edited once a VAT return has been locked. However, an invoice is a legal document between you and your customer if it’s been sent to them and if it needed changing we would normally recommend you create a credit note, net it off with the historic invoice and then create a new invoice.
In certain circumstances, for example, if you hadn’t actually sent the invoice to your client, or if you simply wanted to allocate the invoice to a different project but had filed it on a VAT return, then you may choose to edit the invoice instead of going down the credit note option.
How edited transactions will be dealt with for VAT
If you edit a transaction in a locked period, FreeAgent will preserve your existing locked VAT return intact, and make any necessary changes on your next unlocked VAT return.
That's how HMRC expect VAT errors to be corrected.
How to make the corrections
Edit your invoices, bills, bank payments and expenses as you would do to correct any other errors.
FreeAgent will then make those changes on your next unlocked VAT return.
Simple as that!