Assuming the key file is stored in the Strongbox documents folder, Apple does not allow App Extensions (which is what AutoFill is) to access the parent App’s documents directory directly. This leads to the situation where Strongbox can see the key file (and use it automatically) but the App Extension (AutoFill) cannot.
The solution to this is to “Import” your Key File instead of leaving it in Strongbox’s Documents directory. You can do this via “Key File Management”. This can be accessed during the unlock screen.
It can also be done via the preferences by following these instructions:
- From the Databases screen, tap the gear icon in the top right
- Scroll down and tap Advanced
- Tap Key File Management
- Tap Import (in the top right)
- Navigate to your key file and tap Import again
- Go back to your list of databases and unlock your database
- Tap the three dot menu in the top right
- Tap Set Master Credentials
- Under the Key File heading, tap Select...
- Choose your key file
There’s another quick fix/work around, which is to use a PIN code or Biometric (Touch ID/Face ID) convenience method to open your database, this means Strongbox can use master credentials stored in the secure enclave (which is also accessible by the Auto Fill extension).