Add new field in access Sequence in Sales Order

Hello ,

I have created access sequence in pricing taking table fields using T.code V/03

Fields are as follow -

VKORG  Sales Organization

VTWEG  Distribution Channel

KUNNR   Customer

MATNR   Material

Now i want add one more field Purchase order number in same

BSTKD - PO number

That means our access sequence like

Sales Organization / Distribution Channel / Customer/ Material /  PO number

Please provide way to add PO number in access sequence and it should affect pricing while we create sales order and in billing if we maintain access sequence in VK11.

Thanks,

vanita