You can spend money from Reserves directly by making a payment from the Novo app and selecting a Reserve from the “Send money from” dropdown.
If you make a purchase or withdraw funds greater than your Available Balance, your Available Balance will show as negative. If your Reserves balances are sufficient to cover the negative Available Balance, your account will not be considered in overdraft. You can bring your Available Balance back to a positive amount by transferring funds from your Reserves or assigning debit transactions from your Available Balance to a Reserve with sufficient balance.