The license is purchased through the application itself.
To make the purchase, you must associate a credit card or a prepaid card to your account: Google Play or Huawei AppGallery for Android and Apple AppStore for iOS.

Some Stores may accept multiple payment methods.

Android applications must be installed directly from an authorized Store (Google Play Store or Huawei AppGallery) otherwise the license cannot be verified. It is not possible to install them manually via apk or restore them with a backup software.

After installation, open the app and go to Settings > License, finally restore the purchased license.

To restore the subscription correctly you must be logged in to the Store with the same account (email address) used for the purchase.

It is not possible to restore a purchase made with another account or using a different Store.

Install the application from the Apple AppStore.

After installation, open the app and go to Settings > License, finally restore the purchased license.

To restore the subscription correctly you must be logged in to the Store with the same account (Apple ID) used for the purchase.

It is not possible to restore a purchase made with another account or using a different Store.

If you have purchased the old PRO version of the app: go to the App Store and click on the user’s logo at the top right. In the tab shown select the item “Purchases” where to search and install the app purchased previously.

Install the application from the Microsoft Store.

After installation, open the app and go to Settings > License, finally restore the purchased license.

To restore the subscription correctly you must be logged in to the Store with the same account (email address) used for the purchase.

It is not possible to restore a purchase made with another account or using a different Store.

Certainly, as long as the account set up on the second device is the same account used for the purchase.
However, it is not possible to purchase an Android license and use it on an iOS or Windows device (and vice versa).
No, you can’t transfer the license.
The app is distributed by three different Stores: PlayStore for Android, Apple AppStore for iOS, Microsoft Store for Windows.
In this case you must purchase a new license.
To cancel the subscription, open the app > Settings > License and select “Manage subscriptions”, at this point you will be redirected to the Store page which will allow you to cancel your subscription.

Alternatively, you can use the respective Stores’ functions directly:
Google Play Store: How to cancel a subscription made through the Google Play Store
Huawei AppGallery: How to cancel a subscription made through the Huawei AppGallery
Apple App Store: How to cancel a subscription made through the App Store
Microsoft Store: How to cancel a subscription made through the Microsoft Store

The apps are available free of charge for Android, iOS, and some for Windows (providing basic calculations and displaying ads), with the option to make in-app purchases to access a PRO version.
The pricing model for the PRO version includes an annual or quarterly subscription that provides access to all advanced calculations and removes ads.
Additionally, each app offers a 7-day free trial to evaluate its capabilities.
The apps only require an internet connection to validate the license; all calculations are performed offline. No user data is collected or shared with third parties, ensuring privacy.