Apple takes a 30% cut of all iOS in-app purchases for digital products and services (but not physical ones). This includes products like a Spotify Premium subscription. Spotify argues that it cannot offer pricing competitive with Apple Music when they have to pay the 30% but Apple does not. Spotify and similar companies can accept payments via other means, but Apple then prevents them from emailing their own customers about updates, etc. Spotify has taken their argument to the European Commission, asking them to rule that these practices constitute unfair competition.
Source: Phone Scoop – Latest News