title: Android GCM SENDER_ID, how to get it?
body: <p>I try to migrate to <code>GCM</code> and I have an issue with the <code>SENDER_ID</code> I need to provide. I use the demo project from google. In this project I need, if I understand this well, to provide a <code>SENDER_ID</code> to the application in the CommonUtilities.java file. </p>
  
  <p>The SENDER_ID I provided is the API key I registered on <a href="https://code.google.com/apis/console/" rel="noreferrer">https://code.google.com/apis/console/</a> and has this form: <code>AIzaSyAxxxxxxx_xxxxxxxxxxxnoGZw</code> (total 40 chars).</p>
  
  <p>Using this string as <code>SENDER_ID</code> I get on "BroadcastReceiver mHandleMessageReceiver" an error message: <strong>From GCM: error (INVALID_SENDER).</strong>.</p>
  
  <p><em>Where is the mistake? The string I provide is not the <code>SENDER_ID</code>?</em></p>
  
  <p>Thank you.</p>