I found the answer with my calendars. I had a calendar called StudioFlat1 and StudioFlat2 and couldn’t get either calendar to show. It was always the default that showed. Then I re-read the instructions. Here’s the answer.
Go to Plugins -> Availability
Here you will see your list of calendars starting with the default one at the top.
For each calendar there is a ‘View’ button.
With the exception of the first (default) calendar there is then a link to delete the calendar.
To the right of that link is the calendar id in brackets.
This is what you have to use in the shortcode and not the calendar name you gave it when you created the calendar.
My ids turned out to be studioflat1 and studioflat2. No capital letters. I also discovered that spaces are replaced with hyphens, and once you’ve created a calendar, it doesn’t matter how often you rename it, the id always remains the same. If you want to change an id you have to delete the calendar and create a new one to get a new id.
The fact that the default calendar always has an id of ‘default’ is a bit of a nuisance but I found that never using this and always creating my own calendars gave me the greatest control. I also booked out the entire year of the default calendar so that I’d know straight away if I accidentally got this on any page. I never have properties fully booked for a whole year.
Hope this helps some people.