<?php

$paypal_data = array(
    'USER' => urlencode('andree_1272823561_biz_api1.gmail.com'),
    'PWD' => urlencode('1272823576'),
    'SIGNATURE' => urlencode('Am1t0wiu2tv7VwZ5ebdeY9zv1GF6Ad0PFz-qTGFFf7vbWU6ee4bxy8KL'),
    'VERSION' => urlencode('52.0'),
    'PAYMENTACTION' => urlencode('Sale'),
    'METHOD' => urlencode('SetExpressCheckout'),
    'AMT' => urlencode('52.00'),
    'RETURNURL' => urlencode('get_express_checkout_details.php'),
    'CANCELURL' => urlencode('index.php')
);

$url = 'https://api-3t.sandbox.paypal.com/nvp?' . http_build_query($paypal_data);
$curl = curl_init();

curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($curl, CURLOPT_CAINFO, dirname(__FILE__) . '/cacert.pem');

$result = curl_exec($curl);
curl_close($curl);
parse_str($result, $result);
?>

<pre>Data sent: <?php print_r($paypal_data); ?></pre>
<pre>Result: <?php print_r($result); ?></pre>

Data sent: Array
(
    [USER] => andree_1272823561_biz_api1.gmail.com
    [PWD] => 1272823576
    [SIGNATURE] => Am1t0wiu2tv7VwZ5ebdeY9zv1GF6Ad0PFz-qTGFFf7vbWU6ee4bxy8KL
    [VERSION] => 52.0
    [PAYMENTACTION] => Sale
    [METHOD] => SetExpressCheckout
    [AMT] => 52.00
    [RETURNURL] => get_express_checkout_details.php
    [CANCELURL] => index.php
)

Result: Array
(
    [ACK] => Failure
    [L_ERRORCODE0] => 81002
    [L_SHORTMESSAGE0] => Unspecified Method
    [L_LONGMESSAGE0] => Method Specified is not Supported
    [L_SEVERITYCODE0] => Error
)