You cannot set URL and security settings in the same operation - if you must set both, set the URL first, then edit the femtofox-config.txt file on the USB drive to remove the URL and add in your security settings.
To add an admin key, copy it from the app and add base64: to the beginning (meshtastic_admin_key="base64:T/b8EGvi/Nqi6GyGefJt/jOQr+5uWHHZuBavkNcUwWQ=").
Clearing the admin key list: The admin key list can contain up to three keys - if more are added they will be ignored. The USB configuration tool supports clearing the admin key list, after which you will need to re-add your admin key/s in a second operation. To clear the admin key list, enter meshtastic_admin_key="0", without base64:.
[!WARNING]
Attempting to set wifi settings via USB configuration tool without a USB adapter connected will lead to a hard crash - you will need to disconnect and reconnect power to recover.