The confirmation you receive from the GCM service only tells you that the message was received by the GCM service, whether it is delivered to the application or not. You will receive it even if the device on which the application is installed is disabled.
If you want to receive confirmation when a message is delivered to the application, you must call your server from your application when it receives the message. You can specify a unique identifier in your message and send this identifier from your application to your server to confirm delivery.
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