You can only use the scan features if you build your own mobile app using the phonegap process. I don't believe it will work with the Mendix mobile app, because it doesn't have the required plugin installed.
You mentioned that it was working on the built app?
If not make sure your Scan button is above the card scanner widget. Also make sure that in your widget you have added the correct class in the setup tab.
Looks like everything else is ok in the setup.
Regards
Simon
This can have a multitude of causes. What would really help is debugging your device using 'remote devices' in Chrome or via adb. Once you have successfully connected your device to your pc, check the console logging for more information on what is causing the issue.