When my Face ID doesn’t work and I have to input my PIN to access the app, it shows my account balance on screen before I’ve input the PIN. I find this really troubling as if my phone was stolen I wouldn’t want anybody to know my bank balance. Can you consider removing this please. It’s a very odd design and unnecessary.
Long press the Monzo icon on your Home Screen and select ‘Require Face ID’. That will completely lock your app from being seen without Face ID.
You’ll get a weird double Face ID scenario as a result, as your phone followed by the app confirms it’s you, but it’s really not much inconvenience if it protects the info you want it to.