RE: 'Buy one get one free' trade agreements?
Hy Alex,
you can use "supplemtanry items".
This is independent of trade agreements. Just define to add one item with the option "free of charge".

The sample shows how to define that item J00016 will be added with quantity = 1 when quantity = 10 of otem J00016 are ordered in in Ourchase Order
Unfortunatelly the supplementary items need to be manual calculated inside a Purchase Order, either on the PO Line or the complete PO.
The supplementary item will the added to the PO without costs.

.