proration mode, DEFERRED, when upgrading or downgrading a user's subscription. https://developer.android.com/google/play/billing/ billing_subscriptions#prorate 6
users to review a pending change to a subscription price. I/O 2018 Grow and optimize your subscriptions with new Google Play features (Google I/O '18) https://youtu.be/x1AYelepG6o?t=1176 10