if($balance >= $due)
    {
        $amount = $due;
    }
    else
    {
        $amount = $due - $balance
    }

    if($balance > '0')
    {
        $data = array(
            'invoice_id' => $invoice_id,
            'balance_pay' => '1',
            'amount' =>
        );

        $this->payment->create($data);
    }