Updates the quantity of one or more line items in the current site visitor's cart.
This endpoint is only for updating the quantity of line items. To entirely remove a line item from the current cart, use Remove Line Items From Current Cart. To add a new line item to the current cart, use Add To Current Cart.
This endpoint checks the amount of stock remaining for this line item.
If the specified quantity is greater than the remaining stock,
then the quantity returned in the response is the total amount of remaining stock.
Note: This endpoint requires visitor or member authentication.