Certain devices require you to configure a pin code before they can be exposed to Google Home.

When performing certain actions, such as unlocking doors, Google will prompt you to verbally provide the PIN code, for example:

You: Ok Google, unlock the front door.
Google: Can I have your pin?
You: 1234
Google: Ok, opening the front door.

You can set a PIN from the plugin settings in the Homebridge UI.

Once you have set your PIN code, restart Homebridge.