Has there been any development on this topic? Is there any other way to integrate other booking calendars to avoid double booking?
Hi there, @Christopher_Teibel 
Could you please elaborate on your use case? Do you mean Event Calendar or Appointment Booking widget?
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The Booking widget. The calendar on the form will not show booked dates.
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You’d like to get the booked slots blocked in the widget, right?
To automatically mark booked slots as unavailable, you need to connect your widget to Google Calendar:
Here’s a tutorial on how to connect your calendar: Syncing Google Calendar with the Appointment Booking Widget.
Check it out and let me know if it helped 
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