In case you reinstall the app or migrate from one device to another within the same platform (either iOS or Android), you might need to restore the purchases you've previously made.
In this case you need to:
1. Access Hudway Settings in the leftside menu.
2. Tap the section Restore Purchases.
If you're not authorized in the app, you'll see a message Authorization required, and will then be transferred to login screen.
3. You'll then see another message, from App Store requesting your Apple ID password. When you enter this, your purchases will be restored.
On Android, you simply need to log in using your Google Play account, tap Restore Purchases, and your purchase will be restored automatically.