import_data endpoint missing or failing

[illpack]

I would like to test Mixpanel to see if it's the right fit for my purposes but I am hitting a wall while trying to import old data.

I am trying to import_data like

mp.import_data(
  api_key='API Secret',
  api_secret='PROJECT_TOKEN',
  distinct_id=username,
  event_name=event_name,
  timestamp=unix_seconds,
  properties=payload,
)

and I keep getting different authentication errors.
Docs state the api_key param is deprecated but it complains if I don't pass it.

Is this method working, or how can we make it work / make the documentation clear?
Thank you,