SurveyMonkey api：未提供授权代码-401

I'm trying to make an application to get responses from survey and then make reports with them. for the purpose I'm using php. This is my code:

<?php
header('Access-Control-Allow-Origin: *');

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, 
"https://api.surveymonkey.net/v3/benchmark_bundles");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET");
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);

$headers = array(
'Authorization: bearer XXXX',
'Content-Type:application/json',
);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$result = curl_exec($ch);
if (curl_errno($ch)) {
    echo 'Error:' . curl_error($ch);
}
echo $result;
curl_close ($ch);

?>

The thing is, I'm always getting the same error message followed by 401. I have a premium account and the authorization code is the one you gets once yo deploy an application. Maybe the code is not correct at all or maybe surveyMonkey is not getting the authorization correctly.