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.
Only certain transactions can be edited in a VAT locked period, namely, bills and bill credit notes, bank payments, and expenses.
Editing invoices in a VAT locked period
Invoices cannot be edited once a VAT return has been locked. In this situation, you would normally need to create a credit note, net it off with the historic invoice and then create a new invoice. The credit note and new invoice would both need to be in an open VAT period.
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 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!