Issue: When attempting to make a payment or use 3D Secure, I am only prompted for a PIN and not Face ID. A fingerprint button is shown in the corner, but pressing it only causes the dialog to briefly disappear before reappearing.
Details to reproduce: With Face ID turned on, attempt to make a payment. Press the fingerprint button.
OS: iOS 12.0.1
Device: iPhone Xs
App Version: 2.20.0
Screenshots: 
That’s a worry, I’m getting my brand new XR tomorrow.
But why you think it should work with Face ID ? They ask for your card pin for extra security ?
Why would they do that? You can obtain the PIN using face ID so there is no extra security.
Well it sounds like a bug. 
Out of curiosity what options do you get on iOS in settings? Fingerprint for auth?
The settings page says “Your face will always be used for payments and other sensitive actions”. But as far as I can recall, I haven’t had a single Face ID prompt from Monzo in the month I’ve owned the phone, just pin prompts.
I should add that I’ve reinstalled the app, and Face ID is working fine on other banking apps.
As for the fingerprint button in the corner of the payment screen, I don’t know if it’s a mistake that it’s there on a phone with no fingerprint reader or if it’s just a generic icon for biometric authentication, but I’m sure it shouldn’t just flash the payment screen on and off!
So, turning “Face ID to unlock app” on gave me an iOS permission prompt to allow Monzo to use Face ID, and after that turning “Face ID for authentication” off and back on made payments work. So Face ID seems fine but maybe there’s something wrong with permissions somewhere?
Im seeing this as well, I don’t recall ever being prompted for face ID when making a payment, which contradicts the message you have screenshot there. It catches me off guard as I’m used to either tapping my physical card or using Face ID for purchases in Apple pay so to input my Pin Seems strange giving the heightened level of security Face ID brings.
Is this supposed to work like this or is this a purposefully made decision. if so the wording needs to be refined to reflect this.
Try turning all the Face ID stuff off, quit the app and turn it back on (or maybe even reinstall the app), that worked for me. Monzo re-requested permission to use Face ID and it’s been fine ever since.
The bug appears to be that Face ID settings can seemingly be switched on without having appropriate system permissions to use Face ID. So it might also be worth checking the iOS settings to see if Monzo has its Face ID permissions turned on.
Mine seems to work, but I do wonder if it needs a button to start the Face ID, as it just authenticates immediately, as i’m generally looking at the phone. So a confirm button, shows the payment, and press to start face id.