There are 3 separate versions of the iReal Pro: one for iOS, one for Android and one for Mac.
 
If you purchased iReal Pro in the iOS App Store, you can install the app on your iPhone & iPad & iPod (you can't install it on your Mac computer as it is a separate app)
 
If you purchased iReal Pro in the Mac App Store, you can install the app on your MacBook & iMac (you can't install it on your iPhone or iPad as it is a separate app)
 
If you purchased iReal Pro in Google Play Store, you can install the app on your Android phone, tablets and Chromebooks (you can't install it on your Mac computer or iPhone/iPad as it is a separate app)
 
If you purchased iReal Pro in Amazon Appstore, you can install the app on your Fire tablet (or into other Android devices, by downloading the Amazon AppStore app, signing in to your Amazon account and downloading your apps you purchsaed from Amazon.) You can't install the Amazon version on your Mac computer or iPhone/iPad.

Mac, iOS and Android are separate platforms with separate billing by Apple, Google and Amazon.
Unfortunately we have no way to transfer licenses between different platforms.
 
When you purchase the app, the transaction is between you and Apple, Google or Amazon. There is no way to transfer licenses between them and even within Apple, there is no way to transfer purchases between the iOS App Store and the Mac App Store.
We don’t have access to their billing, we don’t have your name either and we receive limited amount of promo codes so we can't fulfill thousands of users' request who are transferring to new devices between different platforms.
 
Thank you for your understanding!