Currently, it is possible to cancel processes through Operate. I would like to know how I can cancel a process by other means, such as an API.
ATT: CAMUNDA 8
You can delete the process the instance using the key. Refer the documentation:
You cannot delete a process without canceling it first. The process must be stopped (canceled) before it can be deleted.
Camunda 8.6 brought a new endpoint to its rest api that resolves this issue.