To restore your in-app-purchase, please:
1. Go to sticker store
2. Tap "My Items"
3. Tap "Restore purchased items"
Or, you can go to the setting page and tap the "Restore purchased items" button.
Please refer to the instruction collage below.
If your purchased items can't be restored through sticker store, please try to purchase it again for FREE. Apple won't charge you again if you had purchased with the same iTunes account.
To restore your in-app-purchase, please go to the Settings page and tap the "Restore purchased items" button in the list. This should restore all items that you have previously purchased using the same Google account.