I've even sent a mail to Spotify and this was their answer:
Thank you for contacting the Spotify Customer Service Team .
If you having this message unfortunately the new app is not compatible with your device,then I am afraid you will have to use the account with other devices , as we have launched the new app for android and some old phones won't be able to use the new app.
We are really sorry about that please accept our apologies ,and thanks for be so understanding.
Please don't hesitate to get in touch with us if there is something else we can do for you.