There is no mechanism whereby Monzo or any other card provider could implement a mechanism that facilitates blocking a merchant as described in this thread.
First, once an amount has been auth’d, even in a pre-auth situation, you the card holder can not change the final settlement amount.
- If you disagreee with the settlement amount discuss the ‘mistake’ with the merchant
- They will usually issue a partial refund for the challenged amount.
Honest merchants will always deal fairly with you.
Trying to use such a capability to dodge paying a tip is just plain mean, fortunately the card schemes make such a use case impossible.
Second, say you are having genuine problems with legitimate transaction concerns, like a merchant double charging and not correcting their mistake, or perhaps a dodgey merchant adding random charges to your account in the hopes that you simply don’t notice (this is where the notification service in Monzo provides significant value), you can raise a chargeback request.
- Chargebacks enable you to claim back money when a transaction is successfully challenged
- You need to be prepared to prove that the chargeback is justified
- If upheld, the merchant will have the money taken from their account automatically and they will also face a significant charge to cover the cost off the chargeback investigation
Remember in most cases once a consumer makes a chargeback claim the merchant has that consumer added to a blacklist so that no future card transactions are possible from that consumer. Should you want to trade with that merchant again in the future it will likely have to be cash only.
There simply is no mechanism whereby such a facility as that requested in this thread could be implemented.