When buying a subscription via the App Store or Play Store, Apple or Google manages payment transactions and price changes. If your current plan's price changes, the new rate will not take effect immediately.
Apple or Google will notify you of any price increase before your renewal date. You must agree to the new price, or your subscription will automatically be canceled after it expires.
If the price decreases, you'll continue paying the original amount until cancellation or lapse. At this point, resubscribing means paying the new lower price.