Item number in billing document not matching with delivery document-reg

Hi All,

In the billing document the item number is coming from Shipment document. ie., there are three deliveries in a shipment. Each delivery has got one line item, ie., 10. These three deliveries are assigned to a shipment, the order in which the deliveries are attached if we take as 10 for first delivery, 20 for th esecond and 30 for the third, In billing document the billing from first delivery is getting the item number as 10, the second delivery's billing document is getting the item number as 20 and the third as 30.

Can someone please reply where and how this is configured?

Thanks and regards,

Tajudeen S.