I have fixed start/end dates set in the future - but it says those dates have passed?

If you've set fixed start and end dates on your booking page but your availability isn't showing up on the live preview or on your live booking page, follow this guide to troubleshoot by checking your maximum booking notice

Navigate to Times & availability > Duration & display. If you have a maximum booking notice that does not encompass your fixed start/end dates, you'll see this error and no availability will show up. Extend the maximum booking notice to open up your availability.