Page after transaction

How to set a custom page which shows after a client has made a transaction. Now a blank page appears with the message: "thank you for your transaction".

Hi,
The thank you page is part of your payment methods, so you'll probably have to edit your payment method's code to do it, her is an example of the paypal pro method :

You would have to edit the file plugins/hikashoppayment/paypalpro_thanks.php remove the code to have:
<?php
$app=&JFactory::getApplication();
$app->redirect($return_url);