Any code that interacts with native functionality (like all Ionic Native wrappers that use Cordova plugins) only works if the platform is loaded and ready. Checking for platform.ready() is one way to make sure this is the case.
Also (but probably not the cause for your problem):
Your Cordova tooling seems to be out of date, which might be causing all kinds of problems.
You can read about how to figure out the current Cordova versions and how to update CLI, platforms and plugins here: https://ionic.zone/cordova/update