The latest Spotify firmware is no longer compatible with the iTeufel AIR /AIR BLUE due to some technical changes. The Spotify Connect support via "Available Devices" within the Spotify app is therefore no longer available. Unfortunately, we have no influence on the firmware changed by Spotify.
Workaround: Connect your external player (e.g. smartphone) via Bluetooth to the iTeufel AIR and then play music from Spotify as usual. Listening to Spotify Free (no subscription necessary) is also possible this way.