Second Approver for the invoice to authorize.

Hi Team, 

It would be great to have the following feature where we have a second approver assigned to an invoice after it has been created.
The reason for this is the second approver must approver the invoice BEFORE it is sent to Xero. You would have a 'send to approval' button for the person raising the invoice and a 'approve/authorise' button for the second approver.

This would allow our team to double check the invoice before it is arranged for payment.It would also be great if we could have an automated email notification once an invoice has been created/assigned for approval.