$gateway = Omnipay::create('Alipay_Express');
$gateway->setPartner('8888666622221111');
$gateway->setKey('your**key**here');
$gateway->setSellerEmail('[email protected]');
$gateway->setReturnUrl('http://www.example.com/return');
$gateway->setNotifyUrl('http://www.example.com/notify');

//For 'Alipay_MobileExpress', 'Alipay_WapExpress'
//$gateway->setPrivateKey('/such-as/private_key.pem');

$options = [
    'out_trade_no' => date('YmdHis') . mt_rand(1000,9999), //your site trade no, unique
    'subject'      => 'test', //order title
    'total_fee'    => '0.01', //order total fee
];

$response = $gateway->purchase($options)->send();

$response->getRedirectUrl();
$response->getRedirectData();

//For 'Alipay_MobileExpress'
//Use the order string with iOS or Android SDK
$response->getOrderString();

$gateway = Omnipay::create('Alipay_Express');
$gateway->setPartner('8888666622221111');
$gateway->setKey('your**key**here');
$gateway->setSellerEmail('[email protected]');

//For 'Alipay_MobileExpress', 'Alipay_WapExpress'
//$gateway->setAlipayPublicKey('/such-as/alipay_public_key.pem');

$options = [
    'request_params'=> array_merge($_POST, $_GET), //Don't use $_REQUEST for may contain $_COOKIE
];

$response = $gateway->completePurchase($options)->send();

if ($response->isPaid()) {

   // Paid success, your statements go here.

   //For notify, response 'success' only please.
   //die('success');
} else {

   //For notify, response 'fail' only please.
   //die('fail');
}