I've experimented with Odoo's manufacturing app for some time now. I find no real documentation of the advanced routing and I just can't get this to work:

1) I create a stockable item I call "product A" and map that to a vendor. Now I can create a manual procurement for it and it will generate a Purchase order. Good.

2) I create another stockable item I will manufacture, and create a BoM for it in which I include only the previous product.

Now, if I try to manually create a manufacturing order and try to reserve material for it, the procurement for "product A" fails with "No BoM exists for this product!"

How do I make the manufacturing route change procurement rule to "Buy" for parts that I don't have in stock and don't manufacture myself?

Obviously I will later try even more advanced MOs, where the BoM is made up of other parts I manufacture myself, which in turn use resources I buy... But that is next :)