Apple risked their resources and created the whole ecosystem before Spotify even existed. It's not like Apple put a gun to the heads of Spotify executives and forced them to use the App Store. It's the executives who reviewed Apple's terms and then decided that investing in Apple's ecosystem would be useful for Spotify.
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How should Apple make a return on its investment? Through apps such as Spotify, who don't want to pay a dime? Through Governments, who are actively trying to sabotage it? Your arguments make it seem like Apple has a choice when trying to monetise a large part of the market. They don't.
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I think you are taking the efforts it takes to build an App store user base as granted. Microsoft is spending billions to build one with nothing to show for it. Google managed to build something half decent and it continues to be envious of Apple.
App Store and iOS existed independently of Spotify. Spotify decided to invest into Apple's ecosystem, by their own conviction. Apple didn't force them. Spotify, as a behemoth, and a large part of their market, probably only exists due to Apple. Therefore, any arguments to the effect of "it is unfair to Spotify" are difficult to consider.
No further payments need to be involved.