Third party scenrio

Hi Guru,

I got the two requirements i am not able to fulfill both the requirement. Both the requirements which is related with third party

1. In case of "Third party scenario" Company can only bill to the customer if Invoice verification part is over. If i tried to to bill to customer without invoice verification system must be throw the error message.

2. In case of third party scenario " Customer is place 20 order qty. and And i created a 20 order qty PO to vendor. But vendor is supplies only 18 qty.

requirement is i do not want change the qty in the sales order. While the Bill to customer (during the invoice time) i want change the qty. How you can archive the goal