Purchase-to-Order (PTO) Procurement 
You can order a product from one or several vendors for one particular customer. In contrast to mass orders for the general market, the product in the purchase-to-order is especially designed for the customer so that it cannot be sold to other customers.
Process
To ensure that Purchase-to-orders (PTOs) are considered in order allocation run (ARun), select the Include Purchase-To-Order checkbox when you execute the ARUN transaction.
In Purchase-to-Order processing, the order allocation run accesses the sales order stock during stock selection. For example, you must choose a stock selection for a PTO that selects the sales order stock MSKA with the stock segment KALAB. The available segments for the stock type MSKA are KAINS and KASPE.
In Purchase-to-Order processing, it is not mandatory to execute an allocation run. To include PTO sales orders in order allocation run, select the Order Allocation Required checkbox in Customizing for Maintain Order Allocation Run for Special Sales Documents under 
Logistics - General 
SAP Fashion Management Order Allocation Run Cross-Applications Shipping 
. You can create a delivery only if you have already executed the allocation.