(22)In addition, to ensure that debit card fees are set at an economically efficient level, taking into account the structure of domestic debit card markets, the possibility to express interchange fee caps as a flat rate should be maintained. A flat rate may also promote the use of card-based payments of small value amounts (‘micropayments’). It should also be possible to apply such a flat rate in combination with a percentage rate, provided that the sum of such interchange fees does not exceed the specified percentage of the total annual transaction value at domestic level within each payment card scheme. Furthermore it should be possible to define a lower per transaction percentage interchange fee cap, and to impose a fixed maximum fee amount as a limit to the fee amount resulting from the applicable per transaction percentage rate.