This feature is available only for Business edition
It's avaiable on page https://admin-api.docs.keitaro.io.
Why some entry-points respond with status '400 Bad Request' on POST request?
A workaround of that behavior is to send an empty post body:
curl_setopt($ch, CURLOPT_POSTFIELDS, '');
Why all the entry points return "404 NotFound"?
You must enable mod_rewrite or setup rewrite paths in Nginx.