Paypal代币错误

我正在设置Paypal订阅-首先我创建令牌，我的示例编码可以在这里看到：

function testing(){
     $urltoken = "https://api.sandbox.paypal.com/v1/oauth2/token";
           $header_token = array(
               'Accept'=>'application/json',
               'Accept-Language'=>'en_US',
           );
           $request_body_token = array(
               'client_id'=>'xxxxxxxxxxxxxxxxxxxxxx',
               'secret'=>'xxxxxxxxxxxxxxxxxxxx',
               'grant_type'=>'client_credentials',

           );
             $take_from_token = wp_remote_request($urltoken, array('method' => 'POST', 'timeout' => 20, 'headers' => $header_token,'body'=>$request_body_token)); 
             var_dump($take_from_token);  

}

这是我得到的响应错误：

array(5) { ["headers"]=> array(8) { ["server"]=> string(17) "Apache-Coyote/1.1" ["proxy_server_info"]=> string(57) "host=slcsbplatformapiserv3001.slc.paypal.com;threadId=850" ["paypal-debug-id"]=> string(13) "09c6fcdc16b91" ["server_info"]=> string(139) "identitysecuretokenserv:v1.oauth2.token&CalThreadId=133&TopLevelTxnStartTime=14c459ad0be&Host=slcsbidensectoken502.slc.paypal.com&pid=28506" ["date"]=> string(29) "Mon, 23 Mar 2015 07:48:35 GMT" ["content-type"]=> string(16) "application/json" ["content-length"]=> string(2) "75" ["connection"]=> string(5) "close" } ["body"]=> string(75) "{"error":"invalid_client","error_description":"Invalid client credentials"}" ["response"]=> array(2) { ["code"]=> int(401) ["message"]=> string(12) "Unauthorized" } ["cookies"]=> array(0) { } ["filename"]=> NULL }