src/Message/ExpressCompletePurchaseResponse.php
public function isSuccessful()
    {
        $success = isset($this->data['ACK']) && in_array($this->data['ACK'], array('Success', 'SuccessWithWarning'));
        return !$this->isRedirect() && $success;
    }
public function isSuccessful()
    {
        $success = isset($this->data['ACK']) && in_array($this->data['ACK'], array('Success', 'SuccessWithWarning'));
        return !$this->isRedirect() && $success;
    }
/*
Is this complete purchase response successful? Will not be successful if it's a redirect response.

@return bool