Rollback ‘Sent’ Invoices to ‘Approved’.
Only Users with the role ‘Invoice Admin’ can ‘roll-back’ the status of Sales Invoices from ‘Sent’ to ‘Approved’ allowing the invoice to be edited and emailed or printed again.
Under the ‘hamburger’ in the top right of the open invoice details screen, there is an option that appears in ‘Sent’ invoices to mark the invoice as un-sent.