If you already paid to unlock everything in Zombies, Run! 5K Training before December 2019, then you won't need to pay or subscribe again.
However, that purchase is tied to the App Store account, or Google Play Store account that you made the purchase with, and it is not possible to transfer that purchase between platforms.
Purchasing the 5K Training app individually also does not grant access to Zombies, Run! or The Walk.
If you're an Android user who bought the app before November 2017, read this.