By default, invoices’ statuses will be set to saved. If a user with the appropriate rights sets the status to approved, then the co-worker with accountant rights will be notified via email.
An invoice with a status "rejected" means that it has any flows, hence it cannot be accepted. In case the invoice is fulfilled, its status is set to paid.
The balance of the incoming invoice is manageable on it. By date, you can set when how much was paid from that invoice, and the system records the remaining amount.