Paypal sand box

[mogahead]

is this need to require the gateway package in composer beside your package or not
when i set testmode to false this is error response haven't redirect ....
when i set it to true the record back with success but the transaction didn't save in sand box transaction or the funds effect this is any reason hear is my code

use Omnipay;

public function getApiInfos() {
  return array(
    'cancelUrl' => URL::route('paypal_response'),
    'returnUrl' => URL::route('success_paypal_response'),
    'amount'    => '50.00',
    'currency'  => 'USD',
    'description' => '#description'
  );
}



public function upgrade_acount_processing()
{

// make paypal payment

$gateway = Omnipay::gateway('PayPal_Express');
    $gateway->setUsername('xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx');
    $gateway->setPassword('xxxxxxxxxxxxxxxxx');
    $gateway->setSignature('xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx');
    $gateway->setTestMode(true);

    $response = $gateway->purchase($this->getApiInfos())->send();
    return $response->redirect();
}