Using Authenticator when Touch ID has failed

My iPhone 6 Touch ID has failed. Now, when I try to use the Microsoft Authenticator (and some other apps), I'm prompted for Touch ID. I have the option to enter my passcode or use Touch ID, but there's no way to enter a passcode (keyboard does not come up). I can't find any way to turn AppLock off without having access to Authenticator first. Vicious circle...

I have checked Settings for Authenticator and there's no option to disable this. I've also removed and reinstalled Authenticator.