When you subscribe to our Pro subscription service through the App Store, you'll keep paying the same amount you originally signed up for as long as you don't cancel your current subscription. It doesn't matter if we change the price of Pro; you are grandfathered into the same price.
If you cancel your Pro subscription and decide to resubscribe in the future, you'll have to pay the new rate.
When you subscribe to Pro through the Play Store, Google will notify you of price changes before your renewal date to decide if you want to continue.