It also means that, if you upgrade to Premium via the Spotify app, Spotify only gets 70% of the $9.99 you pay every month. That's why it jacked the price up to $13.99 for awhile, while keeping the $9.99 price for users who signed up on the Spotify website. Ultimately, to stay competitive with Apple Music, it lowered the prices back down -- but got creative about encouraging new users to sign up outside the app, launching a promotional campaign that rewarded new subscribers with a discounted trial period -- as long as they signed up via the website.
Spotify gave Apple the middle finger, so Apple blocked Spotify's app update
Apple called foul. There's a clause in its developer rules that mandates apps cannot offer codes or encouragement to side-step Apple's in-app billing mechanism, so they threatened to remove the Spotify app from the store unless it complied.
This is where things get heated. In its last app update, Spotify removed mention of the promotion... but also turned off its app store billing option, completely. If you updated your Spotify app recently, you'll notice that its devoid of your credit card information, and there's absolutely no method of paying for Premium if you're a new user.