The shipping cost is paid when confirming your order (unless the customer decides to use their own courier or shipping service). You will not be asked to pay it again for the same order. However, in some cases, the courier may request payment of custom fees before releasing the order for delivery.
Please note that custom fees are regulated by the tax laws of the destination country and are completely separate from shipping costs. These fees are the responsibility of the customer and must be settled directly with the customs authority.