Hi Binh,
Thanks for reaching out. That error coming from the Octopus Server indicates that the PUT request is invalid. specifically that the endpoint address must be specified.
The best practice for updating object via the API would be to query the object, like you are doing in the GET request, and then use the whole JSON object in the body of the PUT when doing the update. i.e. take the whole machine object from your query, update the required fields and then put the whole JSON object in the body for the PUT request.
I hope that helps, please let me know if you have further questions.