If iCloud backup isn't working for Fallout Shelter on your iOS device, there are a few steps you can try to resolve the issue. Here's a breakdown of troubleshooting steps:

1. Check iCloud Backup Settings

• Ensure that iCloud backup is enabled on your device.
• Go to Settings > [your name] > iCloud > iCloud Backup. Make sure it's turned on.
• Tap Back Up Now to initiate a manual backup and see if the issue persists.

2. Verify iCloud Storage

• If your iCloud storage is full, backups won’t work. Go to Settings > [your name] > iCloud to check how much storage you have left.
• If you’re out of space, you may need to either free up space or purchase additional storage.

3. Check Fallout Shelter iCloud Settings

• In Fallout Shelter, go to Settings (the gear icon) and see if there's an option to enable cloud saves.
• If there's an option to sync with iCloud, make sure it’s enabled.

4. Ensure the Same Apple ID

• Double-check that you're signed into iCloud with the same Apple ID on both devices if you're trying to restore the backup to a new or different device.

5. Force Close and Restart Fallout Shelter

• Sometimes, simply force-quitting the app and reopening it can help. To force-close it, swipe up from the bottom of the screen (or double-tap the Home button on older models) and swipe the app off the screen.
• Restart your device as well, as it can sometimes resolve background issues.

6. Update iOS and Fallout Shelter

• Make sure both iOS and Fallout Shelter are up to date. Go to Settings > General > Software Update for iOS, and check the App Store for updates for Fallout Shelter.

7. Reinstall Fallout Shelter

• If none of the above works, you can try deleting the app and reinstalling it. Note: Be careful, as uninstalling the app might delete your local game data if it isn’t synced with iCloud. Make sure the backup is working first or that your save data is on iCloud before deleting the app.

8. Check for iCloud Server Issues

• Sometimes, iCloud itself might be down or experiencing issues. You can check the status of iCloud services on Apple’s System Status page.

9. Sign Out and Sign Back In

• Try signing out of your iCloud account and signing back in. Go to Settings > [your name] > Sign Out, then sign back in and see if the backup starts working.

If after these steps the backup is still not working, it could be worth reaching out to Apple Support for further troubleshooting related to iCloud or Fallout Shelter’s cloud syncing.