As I don't have a rooted device (and so couldn't just drop the MonetisationVars into the right folder), I decided to get this working in a very long way.
Downloaded Android Studio on my PC, connected the phone to the PC via Bluetooth, used wireless debugging and paired my phone with Android Studio, and opened up a shell on the phone with adb, allowing me to copy the file into the folder.
Very roundabout way, but it had me learning how to get adb going wirelessly, and it works a treat.
Works now, thanks Sbenny