Best practice for collecting a response from a third party
After the payment has been made, you can have the response callback go to an anonymous action method on your plugin's controller.

The URL for that would look something like this:

http://mydomain.com/index.php/actions/myPluginHanlde/myPluginController/myPluginAction


From there you can perform any additional business logic (validation, record saving, etc.), and $this-&gt;redirect(''); to a success template.