If the alert "You've already purchased this but it hasn't been downloaded. Tap OK to download it now." shows up, most of the time that means that the purchase has not gone through. Please perform the following steps to fix this.
1. Completely close and reopen OurSong's app.
2. Click on the "Buy OurCoin" button, and hit "Refresh".
3. Proceed to purchase OurCoin as the problem is solved.
4. If the problem remains, reinstalling the app should do the trick. Or you can always contact us at firstname.lastname@example.org, we should be at your service!