When I try to suspend/activate a process instance by id, it always returns 204 no matter the inputs I supply in the request.
For example, the following request returns a status of 204:
PUT http://localhost:8080/engine-rest/process-instance/this-id-do-not-exist/suspended

In addition, the request above doesn't require the "suspended' parameter in the request body. The response is the same whether the "suspended" parameter is present or not.