403 on OAuth device flow against staging API

Hi,
I'm trying to use the Trakt staging environment and hitting a 403 when calling POST on `/oauth/device/code` with a `client_id` and corresponding secret that were registered on staging.
I'm using `https://staging.trakt.tv` as the `api-staging.trakt.tv` host doesn't seem to respond to this request.
What am I missing?
Thank you.