https://wccftech.com/spotify-files-eu-antitrust-over-fee-in-the-apple-app-store/

Spotify claims that the pricing model in the App Store favors Apple services giving them an unfair advantage in the marketplace.

Invisible to the customer is the fee apple takes when purchasing in the app store or a subscription within an app. This fee is largely responsible for Apple’s $10 billion in services revenue per quarter, with relatively small amounts from licenses (default search engines etc.), subscriptions such as Apple Music, and Apple Pay and Apple Care for the remaining. This fee was 30% of app sales until 2016 when it was lowered to 15% on subscriptions.