If you have tried installing the Cardsave Magento module and IWD one step checkout modules together you will find that the customer is notified of failure, even though the transactions are successful
You may see a message similar to “Your payment attempt has been declined by your issuing bank. Please check your credit/debit card details and try again.”
This is due to the modules both trying to extend the same class
class Cardsave_Sales_Model_Service_Quote extends Mage_Sales_Model_Service_Quote[/code]
class IWD_OnepageCheckout_Model_Service_Quote extends Mage_Sales_Model_Service_Quote[/code]
How to Fix
One of the ways this can be fixed is by changing the IWD Class to extend the cardsave class, this can be done easily by editing the following code
class IWD_OnepageCheckout_Model_Service_Quote extends Cardsave_Sales_Model_Service_Quote[/code]
Everything should work fine now.
This fix was tested in IWD Module Version 2.2.4, Cardsave Module Version 1.14.4, and Magento 220.127.116.11
Just remember, when upgrading extension, you need to make sure you test and solve conflicts again.