When you take a payment with the Mews terminal, you have the option to also cancel it directly from the terminal.
When you cancel a payment using the Mews terminal, the payment is marked as Pending in Mews for a few minutes, which is the time that takes the merchant provider to send an update to Mews. The payment is then marked as Canceled in Mews too.
If the payment doesn't change to Canceled after a couple of hours, contact the Mews Support team. Contact Customer Support