Users of Pacemaker who are on the T-Mobile mobile network may be unable to login to Spotify.
Workaround: Switch to a WiFi network.
T-Mobile offer a Music Freedom service which is meant to let you listen to Spotify tracks for free without charging you on your mobile bill. Their system appears to affect Pacemaker and other third party apps which link to Spotify based on reports we've seen online.
We've reported this to T-Mobile, but are unable to fix this ourselves.
You may have more success if you personally contact T-Mobile and share the following thread with them:
If you are not a T-Mobile customer, you likely have another issue. Please open a thread and we'll be happy to help.