Rake import category doesn't respect parent category

I’m following @tshenry’s excellent guide to bulk import categories. It works, except it puts the new category at the top level, not under the parent category I specified. I know the parent category 72 is valid- I generated this json by tweaking exported json (as a way of nearly-copying an existing category).

{"categories": [{"auto_close_based_on_last_post": false, "user_id": 1, "name": "New York City Meetups", "permissions_params": {"NewYorkCityMeetupGroup": 1}, "color": "0088CC", "auto_close_hours": null, "all_topics_wiki": false, "parent_category_id": 72, "topic_template": null, "text_color": "FFFFFF", "description": null}]}