I would like to add an AirBNB listing where the owner already has bookings. I need to transition this listing to my API. What is the best way to do this? Would I just link the calendar, then add the listing to API so any new bookings were API?
You can add a second Airbnb API connection, to the other owner's Airbnb account:
https://www.ownerrez.com/support/articles/channel-management-api-integrations-airbnb-common-issues-questions#multiple-accounts
That will bring in all the bookings. Then you can run Channel Bridge against their account to bring in past and payment data.
https://www.ownerrez.com/support/articles/channel-bridge-bringing-in-bookings-from-channels