too long

I am using the AWS php SDK to send SNS messages. I am using APNS. I have followed the SDK examples, no problems there. Most of my messages are getting sent, but some appear to be failing. According to the SNS doc, if I get a message ID back - which I am every single time - then the message has been saved to the queue. How do I get more detailed information about these failed messages? The messages are obviously failing in the attempt to send between AWS and APNS.

$result = $client->publish(array(
    'TopicArn' => 'string',
    'TargetArn' => 'string',
    // Message is required
    'Message' => 'string',
    'Subject' => 'string',
    'MessageStructure' => 'string',
));