Let's imagine a 3 level BOM
Item A101 - FG assembly
Item B202 - Sub Assembly with purchased items
Item C300 - A purchased Item
For you to generate a planned purchase order for Item C300 then all three Items (A101, B202 and C300) need to have a replenishment system (eg B202 would be production order) and a Reordering Policy (eg: B202 might be Lot for Lot)
If B202 has no reordering policy OR has the wrong replenishment system you won't end up proceeding all the way to C300.
Also the BOM need to be assigned to the item(s) that have a BOM.
The best thing to do is open A101 in items and look at Bills of Material|Cost Shares which will show the multi-level exploded BOM. If you don't see B202 or C300 on that list, then the BOM might be missing or the replenisment system isn't setup correctly.
Does that make sense?
