This is the key issue spotify has, Apple music is not playing by the same rules, in fact their monopoly on the app store its undermining Spotifies fair competition.
Its undermining it becuase Apple Music a direct competitor of Spotify effectivly doesnt pay the 30% Apple tax which makes it hugely cheaper.
If Spotify dodge the tax to make it able to compete on price, then Apple then abuse the monopoly it has on the store to prevent Spotify from advertising a premium option, it prevents them from offering or completeing the upgrade, it prevents them from linking to a landing page to describe Spotify business model, it prevents them fron doing anything or Apple will pull the app off the store.
The only way Spotify could "compete" if it takes the 30% on the chin, dramatically reduce its profits and investment it can make compared to Apple Music and it will be bullied down.
There are other arguments here to with Apple slapping restrictions on Spotify, not allowing for years to release an Apple Watch app etc but they are grey.