<form>
            orderId: <input type="text" name="orderId" value="<?php 
if (isset($_REQUEST['orderId'])) {
    echo htmlspecialchars($_REQUEST['orderId']);
}
?>
"><br/>
    <input type="submit">
<input type="hidden" name="go">
</form>
<?php 
include '../infusionsoft.php';
include 'testUtils.php';
if (isset($_REQUEST['go'])) {
    $out = Infusionsoft_InvoiceService::getInvoiceId($_REQUEST['orderId']);
    var_dump($out);
}