Failed to install 'plugin.google.maps':Error: Variable(s) missing: API_KEY_FOR_ANDROID

I have an ionic project it works fine, but when I try to run this 

ionic platform add android

I get this error :

Failed to install 'plugin.google.maps':Error: Variable(s) missing: API_KEY_FOR_ANDROID
    at C:\Users\RSone\AppData\Roaming\npm\node_modules\cordova\node_modules\cordova-lib\src\plugman\install.js:
299:23
    at _fulfilled (C:\Users\RSone\AppData\Roaming\npm\node_modules\cordova\node_modules\q\q.js:787:54)
    at self.promiseDispatch.done (C:\Users\RSone\AppData\Roaming\npm\node_modules\cordova\node_modules\q\q.js:8
16:30)
    at Promise.promise.promiseDispatch (C:\Users\RSone\AppData\Roaming\npm\node_modules\cordova\node_modules\q\
q.js:749:13)
    at C:\Users\RSone\AppData\Roaming\npm\node_modules\cordova\node_modules\q\q.js:557:44
    at flush (C:\Users\RSone\AppData\Roaming\npm\node_modules\cordova\node_modules\q\q.js:108:17)
    at process._tickCallback (node.js:419:13)

To install this plugin on PhoneGap, you need to prepare your API keys for both Google Maps Android API v2 and Google Maps iOS SDK. Inustrctuions how to do it are here: https://github.com/wf9a5m75/phonegap-googlemaps-plugin/wiki/Phonegap-Usage

Even I got same error while installing Google Map plugin. I installed it by phonegap method rather then cordova way.

First if you have tried installing plugin. Check it in plugin list. I don't kow in ionic, but in cordova its 

cordova plugin ls

If Google maps plugin is installed then uninstall it.

Now Download Folder as given there.Google Map Plugin

Extract and edit API Keys in plugin.xml (Refer https://github.com/wf9a5m75/phonegap-googlemaps-plugin/wiki/Phonegap-Usage#5-install-this-plugin)

later Install it using local plugin -

cordova local plugin add (path to the plugin)/phonegap-googlemaps-plugin-master/