Here are some methods to cancel your subscription; this will be different depending on the device you initially signed up on:

Android (Google Play): https://support.google.com/googleplay/answer/7018481
Apple (App Store): https://support.apple.com/118428

Example: If you are subscribed on an Apple device, and then switch to an Android in the future, you can still use your subscription. However, if you want to cancel after the switch, you'll need to cancel the payments through Apple.

Thanks for trying Halfbrick+. You can unsubscribe and resubscribe at any time.