Smartbnb requires you to have an Airbnb password, and to login to Airbnb with that Airbnb password. If you are currently using Google, or Facebook, or any other social authentication method to connect to your Airbnb account, this authentication method is not compatible with Smartbnb.
It's easy to create your Airbnb password: just go to https://www.airbnb.com/forgot_password and include your Airbnb email address.
You will receive instructions by Airbnb on your email to reset, or create, your Airbnb password.
Once this is done, you can connect your Airbnb account to Smartbnb: just add your credentials on https://app.smartbnb.io/account/channels.
You can add as many accounts to Smartbnb as you would like!