Update ListingDuration

Hi, there! I'm updating an element with the ReviseFixedPriceItemCall. I would like to update the announce duration as well. In the API call, even when I set the announcement duration up in 3 days, the actual duration doesn't change. How can I set it up correctly? Thanks a lot for your help


string annToUpdate = TxtAnnCode.Text;
ApiContext apiContext = GetApiContext();
ItemType item = new ItemType();
item.ItemID = annToUpdate;
item.Title = "update ann. title";
// Listing is valid for X days
item.ListingDuration = "Days_3";
// Listing type and price
item.ListingType = ListingTypeCodeType.FixedPriceItem;
item.Currency = CurrencyCodeType.EUR;
item.StartPrice = new AmountType
{
	currencyID = item.Currency,
	Value = 20.00
};
ReviseFixedPriceItemCall apicall = new ReviseFixedPriceItemCall(apiContext);
StringCollection deletedFields = new StringCollection();
apicall.ReviseFixedPriceItem(item, deletedFields);
string itemID = item.ItemID;