Where a card-based payment transaction is initiated by or through the payee and the amount of the transaction is not known when the payer authorises the transaction -
(a) the payer's payment service provider may not block funds on the payer's payment account unless the payer has authorised the exact amount of the funds to be blocked; and
(b) the payer's payment service provider must release the blocked funds without undue delay after becoming aware of the amount of the payment transaction, and in any event immediately after receipt of the payment order.