I have a virtuemart shop in joomla 2.5. I use the authorize.net payment system. My problem is I am not able to configure or add the thank you message after the buyer clicks on confirm purchase.
I hope you are using VM2.x,
You can use common Joomla overrides for thank you message on VM.
The main Order confirmation message can be found at
components/com_virtuemart/views/cart/order_done.php
This page can be override using normal Joomla ways.
templates/your_template_folder/com_virtuemart/cart/order_done.php
Or you can just rewrite message using language files.
COM_VIRTUEMART_CART_ORDERDONE_THANK_YOU
found at language/en-GB/en-GB.com_virtuemart.ini
Hope this helps..