Help with discounted subscriptions for select users (Not free subscriptions/promo codes)

I’m trying to run discounts similar to what Spotify does for students. As far as I can tell Spotify allows a $5 per month subscription for iOS users but the regular subscription cost is $10 per month, but everything I have read and seen indicates this isn’t possible and only free subscription “promo codes” can be given to app users (and only to a limited number of users). What method does Spotify use to give discounted subscriptions (This becomes especially perplexing when it comes to Android apps since they don't allow third party payment software)? Any enlightenment would be deeply appreciated.