@Que13214
If your are manually syncing, then I usually suggest you don't use Instant Book. Most Hosts don't know the manual sync is NOT instantaneous and can even be delayed by 3 hours according to Airbnb. Most Hosts manually refresh the calendars after receiving a booking to force the sync. We had the sync fail several times between Vrbo and Airbnb and stopped using Instant Book because of that to prevent double bookings.
Calendar Sync
https://www.airbnb.com/help/article/99
Refresh Calendar
Your Airbnb calendar automatically updates every 3 hours, and pulls in information from the other calendars you’ve connected. To check your latest availability sooner than 3 hours, you can go to your connected calendar and select Refresh.If you’ve connected multiple calendars, they may automatically update at different times. We’ll show the latest time that each calendar was updated, and you can manually refresh them as well.