You need not pay.
During the installation process, you will be prompted for the email and password from your account.
Use this help:
How to uninstall: https://www.hoverwatch.com/faq/how-to-uninstall-hoverwatch-for-android
Please check on your target device, that setting "Unknown sources" is enabled.
If "Open" button is disabled, please dial ***0000### after installation. It should open Hoverwatch app and you can reactivate it.