How to upload android react-native app to hockeyapp

How do I build the react-native app so I can test it in hockeyapp without being connected?

I'm using react-native-hockeyapp and successfully built the app, which listed it on hockeyapp, but now with the hockeyapp changes:

It does not run on a connected device with run-android and I get a white screen and no console debug messages anymore.
When I uploaded the app_Debug.apk to the hockeyapp by dragging it on the website, I got an invite. Run it on my device and get the white screen and the following two errors:

a. unable to load script from assets 'index.android.bundle'. Make sure your bundle is pakcaged correctly... It then shows a white screen.

b. If I shake and press reload it says: could not connect ot development server. I don't want to connect to development server. I want to test it disconnected!
1. How do I build the app? In Android Studio? Any pointer to instructions?
2. And how do I preserve the possibility to react-native run-android so that I can test it locally and debug quickly for development?

Solution

I created a keystore and then went to myproject/android folder and gradlew assembleRelease