Apple also forbids Spotify and other developers from alerting users that they can sign up for a subscription or complete a purchase outside of its iOS app, and disallows Spotify from advertising deals to its customers in the app or by email, as these practices would circumvent Apple's in-app purchase system.
I assume this is the issue? just get rid of this passage ...
Not only that, but I remember in the late '90s when malls were scared to death of the internet and what it meant for online shopping, and by extension brick and mortar stores. There were strict rules for merchants about not advertising their online stores in the malls. Gap was not allowed to use bags that had gap.com on them, for instance. That lasted about a week it seems (probably about two years, really). This feels about like the same thing. Apple shouldn't restrict their merchants from emailing customers about their online deals OUTSIDE of the App Store.