While logged into Juvonno as a Level 2 Administrator you have access to "Closed Periods".
Go to Accounting.
Close Period: When you select this option you will select the dates you want to close. You will only close periods if you do not wany any further action to be taken against any invoice.
Closed Periods: Show what periods you have closed.
If you close a period you will NOT be able to edit any invoice or void it.
You will only be able to apply a payment against it.
Refunds, Editing the closed period invoices.
If you need to edit one of these invoices you will have to create a Quick Invoice and apply a refund against it.
See Articles on how to Refund.
You can then create the invoice from scratch.