I don’t think the problem is the expression, the problem is that the data isn’t loaded yet at the moment the calendar initializes. Put the calendar creation in a function and call it on the load event of the serverconnect.
If you want to use the serverconnect action directly in the calendar, use the url of the serverconnect and in the server connect add an action step Response at the end, that outputs only the array. You could also use the start and end query parameters to filter your results.
