Symptom: On a date-range field, you pick a check-in and check-out and it says the dates are taken, but when you look at your calendar those days appear open.
Three things cause this, in the order we see them most often.
1. Your calendar is hiding weekends
Many Google Calendar views are set to show Monday through Friday only. If the booked night falls on a Saturday or Sunday, you will not see it, but the plugin still counts it. Switch your Google Calendar to a Month or Week view with weekends shown, then look again. This is the most common version of this problem.
2. You are looking at a different calendar than the field uses
The DrezSync Booking field points at one specific calendar. It is often a secondary calendar with a long address ending in group.calendar.google.com, not your main personal calendar. If you are viewing your main calendar, it will look empty while the real booking sits on the secondary one. Open the DrezSync Booking field, note the Google Calendar ID, and make sure that is the calendar you are viewing. In your calendar’s left sidebar, tick that calendar so its events show.
3. A single night inside the range is booked
A range needs every night free. If you ask for the 24th through the 28th and only the 25th is taken, the whole range is refused, even though the 24th is open. Look across the entire span, not just the first night.
How to be sure
Pick a short range on dates you know are clear, a few weeks out, with weekends visible in your calendar. If that goes through, the earlier refusal was a real event you could not see, usually a hidden weekend or the wrong calendar.