When you view a direct debit in the iOS app while “Face ID for authentication” is enabled in the Monzo settings, and you select “Cancel Direct Debit”, the direct debit is immediately cancelled with no confirmation or warnings. It feels like there should be a warning screen to check whether you really want to do this.
People sometimes cancel their direct debits thinking (wrongly) this will also cancel the underlying service, and are then hit with charges for non-payment, so some sort of explanation of why you might not want to do this could be useful. Some may just tap the Cancel button accidentally…
The current flow probably made sense when direct debits were first introduced on Monzo as the biometric authentication was just Touch ID back then, so moving your thumb to the fingerprint reader served as the confirmation. Now that most iPhones are using Face ID, all that’s required is that you’re looking at the screen in the split second after tapping the “Cancel Direct Debit” button - which of course you will be - so this effectively serves as no confirmation at all.