Not subtracts the goods from the Items section

Hello! 

I added several items (goods) by 2pcs. in the Items section.

Next: in the Costs section made an invoice to pay the supplier for this products and made a payment (status paid).

Next: I added the customer with all the necessary data.

Next: in the Profit section I created an invoice for this customer with the addition of this goods and set the payment (status paid).

In the reports there is a purchase from the supplier and the sale to client, however, the quantityr of goods did not decrease in the Items section.

How to make for goods subtracts from the Items (from the warehouse)?

I would be very grateful for the answer!