Creating the app user using php always throwing the "invalid_request_parameters" error?

I'm trying to create the app user using php. So I have made the following code. But always it throws the 400 error. The same thing I have tried with linux curl, app user is creating. But with php is the problem.

$data = array(name=>nm,is_platform_access_only=>'true');
$header = array("Authorization: Bearer ");
$ch = curl_init("https://api.box.com/2.0/users/");
curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch,CURLOPT_POSTFIELDS,$data);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$response1 = curl_exec($ch);
curl_close($ch);