How to apply discount and recalculate order via api?

Question

1C-Bitrix

It uses its own basket template in Bitrix.
You need to implement a field for entering a discount. This is bullshit.
But the catch is that I can not understand how this is done using api.
There are order recalculations in the developer's documentation.
But while the goods are in the basket, because there is no order id, and I need to recalculate after entering the coupon, when the goods are in the basket, but before placing the order.