Stuck in challenge 2 with the above issue. Below is my code.

orderTrigger  -------- 

/**
 * @name orderTrigger
 * @description
**/
trigger orderTrigger on Order(after update) {
    try{
        if(Trigger.isUpdate && Trigger.New != null){
            OrderHelper.AfterUpdate(Trigger.New,Trigger.old);
        }
    }catch(Exception e){
        System.debug('Exception in trigger -- '+e.getMessage());
    }
}


OrderHelper  --------


public with sharing class OrderHelper {

    /**
     * @name AfterUpdate
     * @description 
     * @param List<Order> newList
     * @param List<Order> oldList
     * @return void
    **/
    public static void AfterUpdate(List<Order> newList, List<Order> oldList){
        Set<Id> orderIds = new Set<Id>();
        for ( Integer i=0; i<newList.size(); i++ ){
            if (newList[i].Status == Constants.ACTIVATED_ORDER_STATUS && oldList[i].Status != Constants.ACTIVATED_ORDER_STATUS){
                orderIds.add(newList[i].Id);
            }
        }
        RollUpOrderItems(orderIds);
    }

    /**
     * @name RollUpOrderItems
     * @description Given a set of Activated Order ids, query the child Order Items and related Products to calculate Inventory levels
     * @param Set<Id> activatedOrderIds
     * @return void
    **/
    public static void RollUpOrderItems(Set<Id> activatedOrderIds){
        //ToDo: Declare a Map named "productMap" of Ids to Product2 records
        Map<Id,Product2> productMap = new Map<Id,Product2>();
        Set<Id> productIds = new Set<Id>();
        
        //ToDo: Loop through a query of OrderItems related to the activatedOrderIds
        for(OrderItem oi : [SELECT Id, Product2Id, Product2.Quantity_Ordered__c, Quantity FROM OrderItem
                            WHERE OrderId IN :activatedOrderIds]){
            productIds.add(oi.Product2Id);                         
        }
        
        //ToDo: Populate the map with the Id of the related Product2 as the key and Product2 record as the value
        productMap = new Map<Id, Product2>([SELECT Id, Quantity_Ordered__c FROM Product2 WHERE Id IN :productIds]);
        
        AggregateResult[] groupedResult = [SELECT Product2Id, SUM(Quantity) activatedQuantity FROM OrderItem
                                             WHERE Product2Id IN :productMap.keySet() GROUP BY Product2Id];
        
        //ToDo: Loop through a query that aggregates the OrderItems related to the Products in the ProductMap keyset
        for(AggregateResult ar : groupedResult){
            productMap.get((String)ar.get('Product2Id')).Quantity_Ordered__c = Integer.valueOf(ar.get('activatedQuantity'));
        }
        
        //ToDo: Perform an update on the records in the productMap
        update productMap.values();
    }

}