Is there a way to add or modify Sales order linked to intercompany.

i have my sales order company 1 selling one item to company 2

then on the company 2 i have the intercompany PO with marking to sales order selling to customer.

I need to add a line on the customer sales order for a part that i have in stock on my company 2, but it is not letting me change anything.

Maybe there is a setup somewhere that i need to modify.

Thanks for your help