Online only means just that: There’s no pre-agreed amount; the merchant POS terminal has to ask the issuer for authorization of any transaction amount, however

Online only means just that: There’s no pre-agreed amount; the merchant POS terminal has to ask the issuer for authorization of any transaction amount, however small. There can be other limits in place (like those controlling whether or not a PIN has to be entered), but those are on top of the requirement to obtain online approval from the issuing bank.