Please use this form to apply for the beta testing. It can also be found on top of the main page of the community (if you click the link there, some fields will be filled out automatically according to your settings in the forum).
Actually you don't need to unsubscribe from the beta: you can just install Spotify from the App Store, and it will replace the (expired) beta version. It's a bit confusing that the beta app just silently quits when expired, but I guess that's something Apple should fix with TestFlight.
I made the mistake and unsubscribed from the beta in TestFlight when the last one expired - how do I get a new invitation so I can resubscribe? I tried my old on and it says invaild. Thanks for the help!