iTunes enforces that an in-app purchase can be made only by the same Apple ID that downloaded the app. This same restriction also applies to restoring purchases, even though you are not purchasing the item again. The "regrant failed" error message suggests that there is a mismatch between the Apple ID used to download the game and the Apple ID being used when clicking the Restore Purchases button.
The fact that you're receiving this message at all suggests that you are currently logged in to the App Store with the Apple ID that purchased the feature (the "correct" Apple ID as far as restoring is concerned), which in turn implies that the app was downloaded using a different Apple ID.
To resolve the problem, please do the following:
- Click the Restore Purchases button and ensure that you're still getting the "regrant failed" message. If you're not getting the "regrant failed" message, switch Apple IDs until you find the account that does get the "regrant failed" message. (This step is primarily to help people who may have switched Apple IDs several times trying to get their purchases restored and lost track of which ID is which. But everyone should do it anyway.)
- Delete the Triple Town app from your device.
- Without changing Apple IDs, re-install Triple Town directly to your device from the App Store app (as opposed to re-installing it by syncing your device with your computer).
- Launch the game and click the Restore Purchases button. You should now no longer get the "regrant failed" message.