The billing document has failed to post as there's no sales order cost estimate - no cost was auto generated through the sales order creation & I now can't create one via CK51n for either PPC4 or ZPC5 as it's complaing about it being non-valuated stock. I then tried the alternative we use for Make to Order on Sales Orders (which are managed as non-valuated stock) & tried results analysis (KKAK) & settlement (VA88) but the sales order isn't recognised as being a cost object to collect costs/revenues, so everything's pretty much stuck. The latter is likely to be the reason why you are having difficulties account assigning the PO to the sales order as it's not being recognised as a cost object.
Please try to explain me what exatly the issue is and looking forward your valuable thoughts
MTO requires Requirement Class assigned with Account Assignemtn category, Costing Variant, Costing, Costing ID and Costing Method and Settlement profile for sales order
Requirement type is in turn linked with Requirment Class.
This requirement type is assigned to Sales order type of MTO.
The finished product which is to be delivered has maintained with all the required componentes in BOM to explode while costing.
So once sale order is created and while saving it will cost the sale order based on the above assignments.
Hope its clear.