Errors
Not found
404 not_found
There is no such object for this key. The same answer covers another organization's id, a project or agent outside a limited key's reach, and a real conversation asked for with a test key — a 404 never confirms that an id exists.
What to do
Check the id, and that the key reaches it: its mode, its projects and its agents.
Retrying
No: the same request gets the same answer until something is changed.