Yesterday, Spotify announced that it has 4m paying subscribers and ‘more than 15m active users’. But the debate around how many more may rumble for a while. Facebook itself claims Spotify has 25.9m “monthly users” – and the vast gap between that figure and Spotify’s own stat can’t help but provoke questions. Facebook’s developer documentation explains that “for apps, people are considered active users if they have visited the app Canvas page; viewed the app on a page profile tab; visited an external website when logged into that site with their Facebook account; or had the Facebook API called on their behalf with an active user session” – the latter being the relevant one for Spotify.