This has been discussed before under: Fingerprint ID problem
However I feel the response wasn’t really fair. During the summer sometimes my fingers can get a bit clammy, which screws up my fingerprint sensor on my phone - meaning I can’t get into the Monzo app.
If it detects there has been multiple failed attempts, perhaps offer to login with your PIN? On the previous thread they suggested simply turning off the fingerprint login - but that’s a bit of a lazy answer isn’t it? It works 99% of the time, but just for that 1% it wouldn’t hurt to have a backup?