What causes the error "There are not enough unallocated items in the cart"?

Question

1C-Bitrix

It is not possible to change the delivery amount through the CSaleOrder::Update() function, the error "Insufficient amount of unallocated goods in the basket" appears. What could be causing the error?

Answer 1

This error occurs when there is a change in the quantity in the basket associated with the order, but the order itself has not been saved. At D7, this moment is solved as follows:
Bitrix\Main\Loader::includeModule("sale");
create an order instance
$order = Order::load($orderId);
get the basket
$basket = $order->getBasket();
change the quantity
foreach ($basketItems as $basketItem) {
$basketItem->setField('QUANTITY', 10); // here we enter the required quantity for the desired product
}
save the basket
$basket->save();
overwrite data in order
$order->refreshData();
save the order
$order->save();