HOWTO: Airspy mini and Airspy R2: Piaware / dump1090-fa configuration

Hi @ all,
I don’t get the Airspy mini to work on my rPI4, so tried again using the current official SD card image “PiAware Image on Raspbian Linux 8.2 ZIP”.
Then I did:
1.) configured wifi and set the IP to 192.168.1.28
2.) enabled ssh
3.) ran the command:

sudo bash -c "$(wget -O - https://raw.githubusercontent.com/wiedehopf/airspy-conf/master/install.sh)"

4.) checked the url to see any flights: http://192.168.1.28/skyaware/

Nothing… no single flight is displayed.
My other rPI3 with the FlightAware Stick is working just fine.

Any ideas what I could have missed!?