Defaulting First Line Customer PO Line number.

Hi Gurus,

We have requirement from business to display sales order first line customer PO line number to get defaulted while creating the second line.

First line details are getting displayed through interface from third party source but at time business cancel the first line and creates the second line manually. While creating the second line manually, the Customer PO number is getting defaulted from header but we want customer PO line number to get defaulted from the first line. Can this be achieved using defaulting rules? Please let me know the conditions which needs to be used.

Secondly, all the mentioned requirement should work only for one particular order source type.