Do I need to buy OnSong for every device I own?

Do I need to buy OnSong for every device I own?

OnSong is purchased on your Apple ID.  If you change devices, it may appear that you have to pay for the app again.  Typically this is because the App Store has not authenticated your Apple ID and does not know that you had originally purchased the app.  Tapping on the buy button will prompt you to sign in and then offer you the download for free.  You could also download a free app first, sign into your Apple ID and then OnSong will appear as a download link.  If you had requested a refund for OnSong, you may not be eligible to download OnSong without repurchase due to a change in Apple's App Store policies.

If you had purchased Add-Ons with OnSong, you can restored them as well.  To do this, tap on the gear icon in the upper right corner of the Menubar to open the Utilities Menu and then choose the Add-Ons option.  Then tap on the Restore Past Purchases button at the bottom of the screen.  You will be prompted to sign into your Apple ID and afterwards, your in-app purchases will be restored.

Since all purchases with your Apple ID and your purchase history, refunds, downloads and installing updates are all handled solely by Apple, you will need to contact Apple App Store Support for further assistance.