I did the ical import and exports to VRBO and Airbnb and did the testing as they suggested before going full API. I am having trouble with bookings made in VRBO showing up to Airbnb calendar and also time blocks made in ownerrez showing up on Airbnb's calendar. So, I deleted my original links for the calendars and started over. It worked...but then when I tried it again with another booking and time block, it is not showing. Any thoughts or ideas appreciated.
Note that, by the nature of the rather old technology involved, iCal calendar syncs are quite slow. They don't sync up immediately when a new event is added - they can take as long as a few hours. This is unfortunately normal, and why we recommend using API connections whenever possible.