Please help me ASP.Net MVC add item to store in controller

[anh34]

I have DirectEvent

        public ActionResult AddItemToDetails(long lookupItemId, String viewBagID, int posLinesCount)
        {
            var itemRepository = new ItemRepository();
            var item = itemRepository.Get(c => c.Id == lookupItemId, new []{ "BaseUom" }).SingleOrDefault();

            Store posLineStore = X.GetCmp<Store>("posLineStore" + viewBagID);
            int lineNo = posLinesCount <= 0 ? 1 : posLinesCount + 1;
            
            var newItem =  new PosLineEditViewModel() { ItemId = item.Id, Description = item.Description, LineNo = lineNo, Quantity = 1, UnitPrice = 1, Amount = 1, UomId = item.BaseUomId, UomDescription = item.BaseUom.Description, Id = 2};
            posLineStore.Add(newItem);
            
            return this.Direct();
        }

Here is my error

Uncaught TypeError: Cannot read property 'add' of undefined
at eval (eval at executeScriptDelay ...