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After getting access token when i try to send Test fax it is showing error, I need help

here is my code for sending fax

if ($platform->loggedIn()){

$request = $rcsdk->createMultipartBuilder()

->setBody(array(

'to' => array(

array('phoneNumber' => '12673314004'),

),

'faxResolution' => 'High',

))

->request('/account/~/extension/~/fax');

$response = $platform->sendRequest($request);

}

and here is the Error