Can not connect to Matrix Voice

I finally installed the Matrix Voice board on my RaspberryPi 3 B on Raspian Stretch Light 2018-04-18 following this guides:

https://matrix-io.github.io/matrix-documentation/matrix-os/getting-started/installation/ https://www.hackster.io/ruchir1674/registration-and-installation-of-matrix-os-110057

Successfully created an account and registered the device. When I now start the service on RPi with: node index.js I get this:

Environment Selected: production
Loading...  device
Loading...  event
Loading...  service
Not using device data from db, using MATRIX_DEVICE_ID and MATRIX_DEVICE_SECRET instead!
Starting as device: d803a860xxxx
hb: sen> [] svc> []
hb: sen> [] svc> []
hb: sen> [] svc> []

On the Ubuntu 17.10 Computer which is in the same network, when I make: matrix list devices

I get:

Device ID          │ Name               │ Description                           │ ok │ Last Online   │
│ d803a860xxxx       │ facinghistory      │ facinghistory                         │ no │ 48 years ago

So my device seems to be not ok and it looks like it was never online. I am also not able to install any app:

matrix install HelloWorld
 ____ | Installing  HelloWorld  ==>  d803a860xxxx
⣽ 
⇒ Installing HelloWorld with policy:
 Installation progress:
Awaiting installation on Device...
 Unable to reach device, the application will be installed as soon as your device is available

Can someone give me some advice on how to bring my Matrix device online and get connected to it? Thanks for any help!

Note: last 4 digits of the device ID changed to xxxx

matrix-io / matrix-creator-quickstart

Can not connect to Matrix Voice #34