Can't Load Fields - Recent Posts

I am using the Appointment Booking Service and displaying the service using the plugin Recent Post.

However, I am unable to load / display fields from the plugin. See attached screenshots. When I click on the fields icon a blank overlay box shows with no labels of fields.

How can I resolve, as I want to display the booking form using the Recent Posts plugin.

Replies are visible only to logged in members with an active subscription.