How to change the total amount in the cart?

Question

1C-Bitrix

How can I add my amount to the total amount in the basket and withdraw it in the basket, in general, change it?
I added my form in the basket, when you enter any amount in the form field and click on the change button, the total amount should change and be added by the amount from the field and move on when placing an order.

What can be used here? Since the amount is not a product, the product cannot be used.

Answer 1

make a custom product that is always available - make its price 1 rub. for example
, do not display it visually in the cart (in an event or result_modifier)
​​when the form is triggered - add goods to the cart by quantity - enter 200 in the form - add 200 of this product
- or change the price of one of goods by setting CUSTOM_PRICE
- or change the price of such a product so as not to set its quantity