Laravel Omnipay with Omnipay / Paypal - Class not found

I am trying to integrate the Omnipay Paypal package with my Laravel 4.1 application. I installed the laravel-omnipay package , as suggested by Omnipay, and followed the instructions to configure it.

I added the laravel-omnipay package for both the array of providers and the array of aliases in the Laravel app.php file. A configuration file has also been created.

My composer.json has the following requirements:

"ignited/laravel-omnipay": "1.*",
"omnipay/paypal": "~2.0"

and the ignited / laravel-omnipay configuration file looks like this:

<?php

return array(

    // The default gateway to use
    'default' => 'paypal',

    // Add in each gateway here
    'gateways' => array(
        'paypal' => array(
            'driver' => 'Paypal_Express',
            'options' => array(
                'solutionType' => '',
                'landingPage' => '',
                'headerImageUrl' => ''
            )
        )
    )
);

But when I call $gateway = Omnipay::gateway('paypal');, I get an error message

Class '\ Omnipay \ Paypal \ ExpressGateway' not found "

Is there something that I forget ?: I