Updates the quantity of one or more line items in a checkout.
This endpoint is only for updating the quantity of line items. To entirely remove a line item from
the checkout, use removeLineItems().
To add a new line item to the checkout, use addToCheckout().
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.
Checkout ID.
Line item info to update.
This method doesn’t return any custom errors, but may return standard errors. Learn more about standard Wix errors.