The API uses a client_id and secret to authenticate requests. Authentication to the API is performed via HTTP basic authentication. Requests made over plain HTTP or without authentication will fail.
Provide your client_id as the basic auth username value and secret as the basic auth password value.
curl -X POST 'https://development.knotapi.com/session/create' \
-u '[client_id]:[secret]' \
-H 'Content-Type: application/json' \
-H 'Knot-Version: 2.0'