You need to enable debugging on your device.
vab uses the adb tool from the SDK - you can check by running adb devices.
Make sure the device has an API level >= the API level used to build the app.
vab will use the highest API level available in the SDK per default. You can change
what API is used with the --api <INT> flag. You can list all API's available with vab --list-apis.
Additionally connect your device via USB to your computer and run vab with the --log flag.
This should capture the logs relevant to the app in question.