"""But my client asks for a solution where they will enter only the sale order and they need invoices based on deliveries. They asked me to check the routines""""
From where system can get the data of Deliveries when you input sales order number in VF01?
When you input sales order in VF01--system thinks it is order related billing--then why Deliveries required?
How come a client can suggest to check in routines where they are completely not aware of what is Routine is?
I think you need to Educate your Client on this requirement.
Phanikumar