The cost of shipping is added automatically when the customer goes to the Checkout; a draft order is created without a shipping fee .
For shared payments, the shipping cost is paid by the payment initiator, i.e. the person who creates a split order.
If there is no initiator (e.g., when manual payment by a merchant is used) or the payment initiator decides not to pay for an order, all shipping costs will be paid by the first recipient that is listed in our Split - Partial Payments pop-up in the cart.
This can be activated if you turn on the appropriate option in the application settings.