adb server’s $ADB_VENDOR_KEYS is not set

While debugging an Android application I wanted to connect to a new device. I factory reset the device and wanted to deploy the application with adb (Android Debug Bridge).

Response from adb after run android –livereload was:

adb.exe: device unauthorized.
This adb server’s $ADB_VENDOR_KEYS is not set
Try ‘adb kill-server’ if that seems wrong.
Otherwise check for a confirmation dialog on your device.

My colleague had the same experience earlier and didn’t know how to solve this. The first entries in google didn’t provide a correct solution.

I tried several first like removing the .android folder from my profile. All effort was unsuccessful.

The solution simply was to allow USB connection on the device via USB debugging in developer options on the Android Device.