[Android] "RSA private or public key is null" error when approving transaction via fingerprint

Issue: I just tried to approve an online transaction (insurance renewal) via the Monzo Android app, but about 300ms after the “Confirm your fingerprint” dialog appears, the “Touch Sensor” part of it is replaced with an “RSA private or public key is null” error.

Details to reproduce:
OS: Android 9.0.5
Device: OnePlus 5T
App Version: I’m a beta tester so presumably it’s a beta version, but the app version is hidden too well for me to able to find it.

Screenshots: The error vanished as soon as I tried the three-finger gesture to screenshot, but I have a video from my camera which is available on request.

@aspiers spie Try disabling authenticate with fingerprint in settings and then enable it again.


Thanks. I’ll try that but I already approved the payment via SMS so I won’t be able to test whether it worked until I find myself in a similar situation again, which probably won’t happen any time soon.

It’s a known issue, work around it disabling and re enabling the feature, I’ve only had it once and never since.


Good to know, thanks. BTW I searched this forum for the error before posting, but got no matches.

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Ye, search isn’t very good I find.

Also usually people just post help I can’t send money or something.


This is probably worth a help topic in app given it happens from time to time and the fix is consistent - that is how I fixed it a few months back


Same for me. Issue happened repeatedly. Turned it off. Did 1 transaction. turned it back to fingerprint. All good again.

In my case an immediate toggle on and off worked. No need to perform a transaction while toggle disabled

Same here.

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I’ve just got it trying to view my card details :pensive:

Just did the toggle and working again :sweat:

That is a new instantiation!

And have you been able fix it by the same approach of toggling off fingerprint authorisation?

Yep :+1:

If it helps with fixing the bug I’m not a beta tester, and on :android:

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Unsure if this is a feature of Monzo app or Android itself, though only seen it for the former - maybe my selection of apps a factor in my experience

I was revealing the card number a couple of times for helping in this thread when it happened.

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I experienced the same issue so I deleted and redownloaded the app and it works again without any problem.

The solution here should just be to toggle off fingerprint authentication and then switch it back on.