Okay so that's great info - thanks Barrett. I'm not sure where you found my organization id? Doesn't appear to be documented, but the url you sent is working! Again, if I make the request without the organization_id filter though... it appears to fail. Not sure why - that doesn't appear to be required in the documentation. But in any case, for my situation that works. Here's my next issue however...
This endpoint works a bit differently from the /search one. /search was pulling all of the parent events, and this new endpoint appears to be pulling all event children - resulting in a much longer list. Now I've looked through the documentation, and the reason for that appears to be the: 'show_series_parent' argument. Makes perfect sense. The problem is that that argument doesn't appear to be working as documented?
By default, 'show_series_parent' is false. And when it is false - I get all of the series children - as expected. So that all looks correct. When I change that argument to true however - instead of getting all series parents I get ONLY the events with NO children. That is:
when 'show_series_parent' is set to false, events with any children do not show as expected. Only events with no children at all appear.