Hello Richard,
You need to check if that plugin is available or not before you invoke any other method from it. In order to do that, you should use the isRecognitionAvailable function inside the plugin:

If you check the code inside of it, not only it validates if the Cordova is defined, but also validates if the plugin is avaible. It is useful to verify if the current application has the plugin installed.

Using this action before calling any other from the plugin will allow you to control what the application needs to do when it doesn't have the plugin available.
Please, be aware that plugins can only be tested in real mobile devices. This means that you won't be able to test them in the browser (like Rahul said), so the return of this action will always be false in the browser.
If you test it in a real mobile device, make sure that you generate new builds for your application with that plugin on it, before installing the APK / IPA files in your mobile devices.
Kind regards,
Rui Barradas