When a payment card is blocked because of an incorrect postcode the Payment Service Provider (PSP) which authorises the transaction must first charge the customer so that they are able to check the postcode held on file by the bank.
When the postcode provided by the customer does not match the postcode held by the bank, the PSP will reverse the charge. Because the charge originally went through, the customer will see it on their statement until their bank processes the reversal, which can take a few business days, depending on the bank.
When the customer repeatedly tries to make the payment this can result in multiple charges that then need to be processed by the bank following the reversal request. Customers will not have access to these funds while the request is being processed by the bank. Whilst this isn't ideal for the customer it is recommended that operators do not turn off requiring postcodes to match, as this helps to mitigate fraud from stolen payment cards.