Usually this error occurs if you set the Strongbox app to require Face ID in iOS 18 or later. This is a new feature with iOS 18 and you might have enabled it by mistake. This additional layer of Face ID check creates a conflict and results in the error you've seen.
You'll need to disable this feature in order to unlock your database with Face ID within Strongbox itself. To turn it off:
1) Go to your iOS home screen
2) Long-press on the Strongbox app icon to bring up the app menu.
3) Tap 'Don't Require Face ID'
Feb 2, 2025