Cannot implicitly convert type 'void' to 'system.collections.generic.list<shopifysharp.order>'

Trying to get data from Shopify by running through loop.

public class OrderList
    {
        public List<Order> orders { get; set; }

    } 



public class Order 
    {
	public Order();

        public long? Id { get; set; }

        public Address BillingAddress { get; set; }

        public string BrowserIp { get; set; }

        public bool? BuyerAcceptsMarketing { get; set; }

        public DateTimeOffset? CancelledAt { get; set; }
    }  



 public List<Order> GetOrdersbyDateRange(DateTime fromdate,DateTime todate)
            {
                var totalorders = new List<Order>();
    
                long? lastid = 0;
    
                while (true)
                {
    
                    var json = _api.Get(string.Format("orders.json?created_at_min={0}&created_at_max={1}&since_id>{2}&limit=250", fromdate.ToString("yyyy-MM-dd"), todate.AddDays(1).ToString("yyyy-MM-dd"), lastid));
                    //var json = _api.Get(string.Format("orders.json"));
                    var searchorders = JsonConvert.DeserializeObject<OrderList>(json).orders;
                    if (searchorders.Count > 0)
                    {
                        lastid = searchorders[0].Id;
                        totalorders = totalorders.AddRange(searchorders);
                    }
                    else
                    {
                        break;
                    }
                   
                }
                return totalorders;
            }

Getting error near this line

totalorders = totalorders.AddRange(searchorders);

Error: Cannot implicitly convert type 'void' to System.Collections.Generic.List<ShopifySharp.Order>

I'm aware AddRange() does not return anything (void), hence the error.
I think m missing some simple point...but not able to fix it.

What I have tried:

Tried using 

<pre>totalorders = totalorders.Add(searchorders);

cannot convert from 'System.Collections.Generic.List<ShopifySharp.Order>' to 'ShopifySharp.Order'