The RunPurchase method is included only for backward compatibility with sites created in Commerce Server 2.0, and will be discontinued in future releases. Use the OrderExecute method of the OrderPipeline object instead of this method.
The RunPurchase method runs the OPP on an OrderForm object that contains the contents of order form storage for the current customer.
Page.RunPurchase(OrderForm)
RunPurchase runs the entire OPP on the OrderForm. If no errors are encountered in the OrderForm, the OPP writes the OrderForm’s contents to receipt storage.