Possibly your (Google) Device ID has changed due to the upgrade. Or you're using another device?
If you can send me the new ID I'll add a signature for that device in the app so you can run it again.
You could try getting the Device ID with:
https://play.google.com/store/apps/details?id=com.skyworxx.sideloadvrdeviceidIt seems that this app doesn't work for Nougat though, please let me know if you can confirm this.
The other way to get the Device ID is to use ADB (Android Debugging Bridge) and run the command ‘adb devices’.
The needed SDK Platform Tools (a 4Mb download) can be downloaded here:
https://developer.android.com/studio/releases/platform-tools.htmlJust unzip the package (for example to C:\ADB), it doesn't need to be installed. Connect your phone with USB.
Then start a command prompt and run: <path to platform-tools folder here >\adb devices
So if you unzipped to C:\ADB then the command will be: C:\ADB\platform-tools\adb devices
You may have to run the command twice. It will then show the device ID for your phone. You can remove the unzipped files/folders after that.
It’s inconvenient that it has to be done like this, but for this stage in development it seems the only way for devices with Nougat. Devices running Android Marshmallow didn’t have this problem up to now.