Plugin triggers in order completion. After the installation, it is added to the group of vmpayment plugins in the Plugin Manager. You can publish the plugin there and also add your code from Heureka. The plugin can also do Heureka converisons but if you don´t use it, leave this field empty.
Since the plugin is added to the group vmpayment, it is also visible in the Virtumart settings, in Payment Methods. You do not need to turn on or set the plugin in Virtuemart.
The plugin contains the code from Heureka, link below:
Heureka – verified by customers
Heureka conversion