Why Android key (api key) is invalid or that key is deprecated by GCM server?
<p>Two years ago (June 2014), I created an Android API key for GCM Push Notification for my Android application. From the last two days, GCM server returns Unauthorized (401) response in PHP.</p>

<p>I searched regarding why GCM server returns 401 to PHP, it mentioned that API key is invalid. Why is the Android API key invalid? If I create a Server key for another application, it works fine.</p>

<p>Is there any validity(lifetime) for Android API key? Which key is the best for GCM push notification? Is it Server, Android, iOS or Browser API key? And do those keys have validity period or not?</p>

<p>Please give the proper details and explanation about those four API keys also their lifetime. Or is Android key deprecated?</p>