In the AspDotNetStorefront admin console, go to Configuration > Site Setup Wizard.
In the Payment Gateway section, click the configure link next to the eProcessingNetwork entry.
Enter the values you obtained from eProcessingNetwork for the Login and Transaction Key.
Click Save and Close.
Finally, click the radio button next to eProcessingNetwork and then click the Save button.
eProcessing Network does not allow voids or refunds on orders that haven't cleared yet. To cancel an order you will need to either delete the authorization through the eProcessing Network terminal, or capture the order through the storefront site and then refund it once it settles.