Automatical update of PO quantity when changed in SO

Question

We have a following issue
for our regular business we have a third party process for trading
goods. So we are using on customer sales order stock. In our system
following is possible: We create a sales order and after using of
Purchase requisition we create a purchase order. So now when we change
the quantity in SO and save the SO, this change is automatically done
in the PO as well.
So this really works without canceling the PO first,
changing the SO and creating a PO again.
So now we have implemented a new product in a different sales area with the same process and
with same material type HAWA but this automatical update of quantity is
not working.
What needs to be done to enable this function for our new
product as well?

Answer 1

My colleague was here when the system was implemented. He is not aware of any development here that enables this function. I have been looking for user exits and none are active for this. I have been told that this works only for customer sales order stock but I was not given any reason why.
It seems logical, that in some development a new sales area needs to be included as Bijay said. Anyway we still think this function works without additional development.
@Raghavendra we are using the SAP standard scenario. SO - PR - PO. PO is manually created out of PR in both cases.