You may have noticed a "Pre-Order button" appear on some product pages, as you can see on the picture below:
If the pre-order button appears, it means that the size you selected in this specific design is currently out of stock but available for pre-order. It is in production in Bolivia and delivery will occur in October or November 2018.
The point of pre-ordering a sweater is to receive it as soon as possible since, once received from Bolivia, some sizes will go out of stock again very fast. The payment is processed when the pre-order is placed.