Why does the app say it cannot verify the license?

To prevent piracy, the app checks online whether the copy you have installed was legally purchased from the Play Store with the Google account you are using. The check is made the first time you start the app, so you have to be online when you first start it. The check is also made later (basically every time you start the app), but the app can be started several times without a successful license verification, so you don't have to be online every time you want to use it.

When you get this message, please make sure you are connected to the Internet and try to start the app again, or press the "Re-Check" button. Also make sure that you are using the same Google account that was used to purchase the app — the app won't run if you switch to another account.

The check is made using Google libraries and services, so make sure you have not blocked Internet access for these services (such as Google Play Services, the Play Store, etc.).

If you tried to copy the apk file from a website other than the Play Store, or you copied the apk from your friend's phone, you are out of luck — the app won't work unless you purchase a legal copy from the Play Store.