get tasks using Rest API

Hi, I have a problem listing the tasks using the Rest API (http://vmware.github.io/vsphere-automation-sdk-rest/6.7.1/operations/com/vmware/cis/tasks.list-operation.html). I want to retrieve the list of tasks for a specific user, so I make the following request:

GET /rest/cis/tasks?filter_spec.users.1=myuser

But I get the following error:

At least one of the parameters 'services' or 'tasks' must not be empty in the filter specification.

But I don't know what value to set in the filter_spec.services.1 parameter. What should I set in the services parameter? Can anyone write an example, please.

Thanks in advance.