Once shop manager received "New Order" email notification.
1. He may click on the order go navigate to single order page
2. Click on "Set Invoice Number & Date" to edit invoice number manually
3. For instance, shop manager can edit invoice number same as order number.
4. Click on the "Update" button to update the invoice number
5. Once you have updated, PDF Invoice will be generated automatically with the manually edited invoice number.
6. If you wish to send invoice to customer. You may choose "Customer Invoice / Order Details"
7. Finally Customer will receive an email with pdf invoice attached to it.
Thanks!