Confirmation Needed: HTTP Request Asset Voice Upload on Free/Trial Plan

Dear HeyGen Support Team,

Please confirm the following point clearly:

Is asset voice upload via HTTP request / API (custom audio upload) restricted or blocked on the Free/Trial plan?

If restricted:

Is this limitation intentional, and
Is upgrading to a paid API plan the only way to enable asset voice uploads via HTTP requests?

A direct yes/no confirmation would be sufficient.

Best regards,
Harry Hams