function pay($payee, $amount, $message = '', $multicall = false)
    {
        $login = $this->getLogin($payee);
        if ($login === false) {
            throw new InvalidArgumentException('payee = ' . print_r($payee, true));
        }
        if (!is_int($amount) || $amount < 1) {
            throw new InvalidArgumentException('amount = ' . print_r($amount, true));
        }
        if (!is_string($message)) {
            throw new InvalidArgumentException('message = ' . print_r($message, true));
        }

        return $this->execute(ucfirst(__FUNCTION__), array($login, $amount, $message), $multicall);
    }