How to put Twilio call on hold or pause using rest api

I'm trying to Implement Twilio call hold functionality from Twilio JS client but the call goes drop/disconnected from the user side.

Below is my code:

$client = new Client($sid, $authtoken);
$call = $client->calls($callSid)->update(
            array(
                "Url"    => 'http://demo.com/Twiml/Hold.php",
                "method" => "POST"
            )
        );
        echo $call->to;

Here is hold.php

<?php 
header("Content-type: text/xml");
echo "<?xml version='1.0' encoding='UTF-8'?>";
echo "<Response>
     <Enqueue waitUrl='wait-music.php'>support</Enqueue>
</Response>";
?>

Here is wait-music.php file

<?php
echo '<?xml version="1.0" encoding="UTF-8" ?>';
echo "<Response>";
echo "<Play>http://com.twilio.sounds.music.s3.amazonaws.com/MARKOVICHAMP-Borghestral.mp3</Play>";
echo "</Response>";
?>

And getting Error:

Twilio/Rest/Client.phpTwilio/Http/CurlClient.phpTwilio/Http/Client.phpTwilio/Rest/Api.phpTwilio/Domain.phpTwilio/Rest/Api/V2010.phpTwilio/Version.phpTwilio/Rest/Api/V2010/AccountContext.phpTwilio/InstanceContext.phpTwilio/Rest/Api/V2010/Account/CallList.phpTwilio/ListResource.phpTwilio/Rest/Api/V2010/Account/CallContext.phpTwilio/Values.phpTwilio/VersionInfo.phpTwilio/Http/Response.phpTwilio/Exceptions/RestException.phpTwilio/Exceptions/TwilioException.php

**Fatal error:**  

Uncaught exception 'Twilio\Exceptions\RestException' with message '[HTTP 400] Unable to update record: No 'To' number is specified' in server_pathTwilio/Version.php:85 Stack trace: #0 server_path/Twilio/Version.php(127): Twilio\Version->exception(Object(Twilio\Http\Response), 'Unable to updat...')