title: cordova-plugin-fcm ERROR : invalid api key
body: <p>I am using <a href="https://github.com/fechanique/cordova-plugin-fcm" rel="noreferrer">cordova-plugin-fcm</a>. I have followed the installation instruction:</p>
  
  <ol>
  <li>install plugin</li>
  <li>add the <code>google-services.json</code> to my root folder</li>
  </ol>
  
  <p>I wanted to test it through their <a href="https://cordova-plugin-fcm.appspot.com/" rel="noreferrer">testing server</a>, but I get the error:</p>
  
  <pre><code>ERROR: invalid api key 
  </code></pre>
  
  <p>The key I inserted was the one from the file <code>google-service.json</code> in the entry:</p>
  
  <pre><code>"api_key": [{"current_key": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"}]
  </code></pre>
  
  <p>How can I do the testing properly?</p>