def coupon_add_payment(payment_method, value, description=u''):
    """
        Add payment method to coupon.
        @param payment_method: The payment method.
        @type payment_method:  a device specific value representing the payment value

        @param value:     The payment value
        @type value:      Decimal

        @param description: A simple description of the payment method to be
                            appended to the coupon.
        @type value:      unicode

        @rtype:           Decimal
        @returns:         the total remaining amount
        """
