<script language="javascript">
function mostrarValue(){

    var selObj = document.getElementById('test');
       var selIndex = selObj.options[selObj.selectedIndex].value;

    }
</script>
<p>Seleccione uno de los articulos</p>
        <label class="youplay-select">
				<select  id="test" name="test">
                <option value="" selected>Seleccionar</option>
                <option value="1000">Articulo1</option>
                <option value="1001">Articulo2</option>
                <option value="1002">Articulo3</option>

            </select>
        </label>


<?php
$cert_id = 'CERTIFICADOPAYPAL';
include("Class.PayPalEWP.php");
$paypal = new PayPalEWP();
$paypal->setTempFileDirectory("tmp");
$paypal->setCertificate("my-pubcert.pem", "my-prvkey.pem");
$paypal->setPayPalCertificate("paypal_cert_pem.txt");
$paypal->setCertificateID($cert_id);

$pp = array(
        'cmd' => '_xclick',
        'cert_id' => $cert_id,
        'business' => 'xxxx@gmail.com',
        'receiver_email' => 'xxxx@gmail.com',
        'custom' => '1',
        'item_name' => $_POST['test'],
         'currency_code' => 'USD',
        'amount' => '1',
        'lc' => 'ES',
        'no_note' => '1',
        'no_shipping' => '1',
        //'return' => '',
        'cancel_return' => '',
        //'notify_url' => '',
        'cbt' => 'Volver al sitio web',


    );

?>


  <form action="https://www.sandbox.paypal.com/cgi-bin/webscr"  id="pay_pal_form" method="POST" name= "form1" onclick="mostrarValue();">

  <input type="hidden" name="cmd" value="_s-xclick"><input type="hidden" name="cmd" value="_s-xclick">
  <input type="hidden" name="encrypted" value="-----BEGIN PKCS7-----<?php echo $paypal->encryptButton($pp); ?>-----END PKCS7-----"/>

  <input type="image" src="https://www.paypal.com/es_XC/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal, la forma más segura y rápida de pagar en línea.">
  <img alt="" border="0" src="https://www.paypal.com/es_XC/i/scr/pixel.gif" width="1" height="1"></p></div>
</form>