Make sure you are using the same app version (Galaxy on Fire 2 HD) and the same Apple ID or Google account used for the original purchase. Purchases made in the older version (Galaxy on Fire 2 SD) cannot be restored in the HD version, as the two apps are separate.

On iOS, go to the main menu and tap Restore Purchases. On Android, purchases should restore automatically if you're logged into the same Google account.

This issue was addressed in the latest update. Please update the app via the App Store and restart your device. Please have a look at the article: Crash in Supernova Challenge – Galaxy on Fire 2 HD (iOS)

Galaxy on Fire 2 HD does not support cloud saving. All progress is stored locally on your device. Without a manual backup, it's not possible to recover your saved data after reinstalling the app or changing devices.

Check the following:

• Make sure your device is not muted (physical mute switch on iPhones).
• Turn up the volume.
• Restart the app.

On iOS, also check under Settings > Accessibility > Audio/Visual and ensure that Mono Audio is turned off.

The game was developed for older devices and may not be optimized for newer models with high refresh rates or unusual screen sizes.
Try the following:

• Close all background apps.
• Restart your device.
• Reduce any available graphics settings in the game.

Double-check that you purchased the expansion in Galaxy on Fire 2 HD, not in Galaxy on Fire 2 SD. If the content was bought in the HD version, use the Restore Purchases button (iOS) or ensure you're logged into the correct Google account (Android).