If you are experiencing issues with restoring the Oxford Advanced Learner's Dictionary (OALD) 9th edition on your device, follow these steps to resolve the problem effectively:

1. Sign Out and Sign In Again
- Open the App Store on your device.
- Tap on your profile picture at the top right corner.
- Scroll down and select "Sign Out."
- After signing out, sign back in using your Apple ID. This process refreshes your account credentials and can help with the restoration of your apps.

2. Using the Restore Option in OALD App
- Open the OALD app once you have logged back into your account.
- Look for the “Restore” button, usually found in the app’s settings or main menu.
- Tap on the “Restore” button to attempt to restore your purchase.

3. Check for App Updates
- Go to the App Store and check if there is an update available for the OALD app.
- If an update is available, tap "Update" to ensure you are using the latest version of the app, which may have fixed previous bugs related to restoration.

4. Network Connectivity
- Ensure that your device is connected to a stable internet connection (Wi-Fi is preferred).
- Try restarting your Wi-Fi router or switching to mobile data temporarily to verify if the issue relates to network connectivity.

5. Contact Support
- If the above steps do not work, consider submitting a support ticket directly to Oxford University Press via their support page here - [learn more].
- Provide them with details about your device, the issue you are facing, and any error messages that may appear during your attempts to restore.

6. Reinstall the App
- As a last resort, you can delete the OALD app from your device and then reinstall it from the App Store.
- After reinstalling, make sure to sign in to your App Store account and then use the “Restore” option again to retrieve your purchase.

Implement these steps sequentially to address the restoration issue with OALD 9th edition effectively. If the problem persists after trying all of the above, it may be necessary to look for further assistance from the app's support team.