Hi Sam,

I had a similar problem to this and it confused me also. This is intended behaviour in that the basket empties.

There are a couple of ways around this.

Firstly in the merchello.config (App_Plugins\Merchello\config\merchello.config) set EmptyBasketOnPaymentSuccess key to false.

  <checkoutContextSettings>
    <setting alias="InvoiceNumberPrefix" value="FT" />
    <setting alias="ApplyTaxesToInvoice" value="true" />
    <setting alias="RaiseCustomerEvents" value="false" />
    <setting alias="ResetCustomerManagerDataOnVersionChange" value="false" />
    <setting alias="ResetPaymentManagerDataOnVersionChange" value="true" />
    <setting alias="ResetExtendedManagerDataOnVersionChange" value="true" />
    <setting alias="ResetShippingManagerDataOnVersionChange" value="true" />
    <setting alias="ResetOfferManagerDataOnVersionChange" value="true" />
    <setting alias="EmptyBasketOnPaymentSuccess" value="false" />
  </checkoutContextSettings>

Secondly is to do this when you create an instance of the CheckoutManager. I had a helper method that did this for me and called this whenever I needed it:

/// <summary>
/// Gets checkoutmanger instance
/// </summary>
/// <param name="customerContext">The context</param>
/// <returns>ICheckoutManagerBase instance</returns>
public static ICheckoutManagerBase GetCheckoutManager(CustomerContextBase customerContext)
{
    var settings = new CheckoutContextSettings()
    {
        ResetCustomerManagerDataOnVersionChange = false,
        ResetExtendedManagerDataOnVersionChange = false,
        ResetShippingManagerDataOnVersionChange = false,
        ResetPaymentManagerDataOnVersionChange = false,
        EmptyBasketOnPaymentSuccess = false
    };

    var basket = customerContext.CurrentCustomer.Basket();

    var checkoutManager = basket.GetCheckoutManager(settings);

    return checkoutManager;
}

Hope that helps

Ben