CodeIgniter，Gocart中的Paypal Express Checkout错误（不支持指定的方法）

Question

我是codeigniter和paypal的新手。我正在研究gocart（一种基于codeIgniter构建的开源电子商务解决方案）。我尝试使用集成在其中的paypal API，但其显示错误如下：[ACK] => Failure [L_ERRORCODE0] => 81002 [L_SHORTMESSAGE0] => Unspecified Method [L_LONGMESSAGE0] => Method Specified is not Supported [L_SEVERITYCODE0] => Error
以下是我的代码： 的 paypal_expres.php

 function __construct() 
{

$this->API_USERNAME ='Username';

$this->API_PASSWORD = 'Password';

$this->API_SIGNATURE ='Signature';

$this->RETURN_URL = 'www.example.com';

$this->CANCEL_URL = 'www.example.com';

$this->currency = 'USD';
$this->host = "api-3t.sandbox.paypal.com";

$this->gate = 'https://www.sandbox.paypal.com/cgi-bin/webscr?';
}


public function doExpressCheckout($amount, $desc, $invoice='')
{

    $data = array(
    'PAYMENTACTION' =>'Sale',    'AMT' => '24',    'RETURNURL' => $this->getReturnTo(),
    'CANCELURL'  => $this->getReturnToCancel(),    'CURRENCYCODE'=> $this->currency,    'METHOD' => 'SetExpressCheckout');    

$query = $this->buildQuery($data);

$result = $this->response($query);

$response = $result->getContent();

$return = $this->responseParse($response);

echo '';

print_r($return);

echo '';

if ($return['ACK'] == 'Success') 
{

header('Location: '.$this->gate.'cmd=_express-checkout&useraction=commit&token='.$return['TOKEN'].'');

die();    }   

return($return);}

public function doExpressCheckout($amount, $desc, $invoice='')
{

$data = array(    'PAYMENTACTION' =>'Sale',    'AMT' => '24',    'RETURNURL' => $this->getReturnTo(),    'CANCELURL'  => $this->getReturnToCancel(),    'CURRENCYCODE'=> $this->currency,    'METHOD' => 'SetExpressCheckout');    

$query = $this->buildQuery($data);

$result = $this->response($query);

$response = $result->getContent();

$return = $this->responseParse($response);

echo '';

print_r($return);

echo '';    

if ($return['ACK'] == 'Success') 
{

header('Location: '.$this->gate.'cmd=_express-checkout&useraction=commit&token='.$return['TOKEN'].'');

die();    }    

return($return);
}

private function response($data)
{

$result = $this->CI->httprequest->connect($data);

if ($result<400) 
return 
$this->CI->httprequest;

return false;}

private function buildQuery($data = array())
{

$data['USER'] = $this->API_USERNAME;

$data['PWD'] = $this->API_PASSWORD;

$data['SIGNATURE'] = $this->API_SIGNATURE;

$data['VERSION'] = '56.0';

$query = http_build_query($data);

return $query;
}