async void OnOrderButtonClick(object sender, EventArgs args)
        {
            var orderSum = orderedProducts.Sum((a) => a.Amount * a.Price);

            var message        = "Are you sure to order for " + string.Format("{0:0.00}", orderSum) + " CHF?";
            var orderConfirmed = await DisplayAlert("Buy products?", message, "Yes", "No");

            if (orderConfirmed)
            {
                var customerPosition = await PositionHelper.GetPositionOrNull(this);

                var response = await App.Rest.CreateOrder(orderedProducts, customerPosition);

                if (response != null)
                {
                    Debug.WriteLine("Created order with id {0}", response.Id);

                    await Navigation.PushModalAsync(new OrderConfirmPage(response));
                }
            }
        }