Yes. As long as you are signed in with the same Apple Account that you used for the purchase or the subscription, you can restore it after changing devices or deleting the app.
If you bought "Ad Removal" as a one-time purchase
- Tap "Settings" in Simple Calendar
- Select "General Settings"
- Tap "Reactivate Ad Removal" at the bottom of the screen
If you subscribe to Premium Service
- Tap "Settings" in Simple Calendar
- Tap "Premium Service" at the top
- Tap "Restore Subscription"
Before restoring, please make sure you are signed in with the same Apple Account you used at the time of the purchase or the subscription.
If the restore does not work, please restart your device and try again. If ads are still shown, please contact us with the details via "Contact Us" at the top right of the Help screen.