If restore button does not work, please check with these steps:
1. iPhone version and iPad version of Recorder Plus are two independent apps. So you need to pay for them separately. So if you have purchased iPhone version, you can not restore the purchase on your iPad.
2.Make sure you have logged in your iPhone/iPad with the SAME Apple ID which is used to install and pay for the app.
3.Make sure network is fine.
Sometimes the network icon indicate the network is fine, but actually it’s not. Please check with accessing Youtube or your other favorite websites.
4.Sometimes Apple’s restore service does not respond in time. So please try the restore button for several more times.
Also you may try the “buy” button. Because the in-app purchase item is non-consumable item.
So if you have purchased the item, then App Store will not let you pay again when tap the “buy” button.