public function setPayment($iPaymentId)
    {
        //  Validate
        $oPayment = $this->oPaymentModel->getById(
            $iPaymentId,
            ['expand' => ['invoice']]
        );

        if (empty($oPayment)) {
            throw new RequestException('Invalid payment ID.');
        }

        $this->oPayment = $oPayment;
        return $this;
    }