Generate checkout link and use with Secret Paypal

paypal_secret.php

<?php
include '../secretpaypal/paypal.php';
$paypal = new SecretPaypal();
$checkoutLink1 = $paypal->getLink('book1.pdf',
        array(
            'amount' => 29.99,
            'item_name' => 'My Book',
            'return' => 'http://house.axcoto.com/example/return.html',
            'cancel_return' => 'http://house.axcoto.com/example/cancel.html',
            )
        );

$checkoutLink2 = $paypal->getLink('mybook.zip',
        array(
            'amount' => 29.99,
            'item_name' => 'My Book',
            'return' => 'http://house.axcoto.com/example/return.html',
            'cancel_return' => 'http://house.axcoto.com/example/cancel.html',
            )
        );

$mp3Link = $paypal->getLink('my_sound.mp3',
        array(
            'amount' => 29.99,
            'item_name' => 'My Book',
            'return' => 'http://house.axcoto.com/example/return.html',
            'cancel_return' => 'http://house.axcoto.com/example/cancel.html',
            )
        );

$pictureLink = $paypal->getLink('picture_cat.png',
        array(
            'amount' => 29.99,
            'item_name' => 'My Book',
            'return' => 'http://house.axcoto.com/example/return.html',
            'cancel_return' => 'http://house.axcoto.com/example/cancel.html',
            )
        );
?>

<a href="<?php echo $checkoutLink1 ?>">
<img src="http://placekitten.com/101/80"><br />
Buy Now
</a>
<a href="<?php echo $checkoutLink2 ?>">
<img src="http://placekitten.com/101/80"><br />
Buy This
</a>
<a href="<?php echo $mp3Link ?>">
<img src="http://placekitten.com/101/80"><br />
Buy This Song
</a>
<a href="<?php echo $pictureLink ?>">
<img src="http://placekitten.com/101/80"><br />
Buy This Picture
</a>