Are there any bugs or issues with the app on version 6.6.3? I have the Add On installed on the indexers and heavy forwarder, I have the Application (Dashboard App) installed on the search heads. The Addon is also on the search heads. Its not populating any data on the Dashboard App.
You only need to install the Technology Add-on (https://splunkbase.splunk.com/app/3457/) on your heavy forwarder; once installed, make sure you set up your input scheduled inside a data input.
The dashboard add-on (https://splunkbase.splunk.com/app/3492/) should be able to work when installed on an active indexer or search head.
Finally, make sure that your data input targets a known index; the default target index is "rapid7".