First, let's check that your login options are set up correctly:

1. Log in to the app with your username and password
2. Go to ‘Account’ (the little cog icon at the bottom of the screen on the right).
3. Check that your face/touch ID access is switched on.

If there's still an issue, this might help:

1. Uninstall the app
2. Restart your phone
3. Reinstall the app
4. Enable access to face/touch ID
5. Log in again

If it’s still not working, then it might be an issue with your phone.
Your phone manufacturer might be able to help.