Update WorkItem status with OSLC API

I'm trying to change workitem status from 'new' to another status like
'Start Working' or 'Complete'.

I read an article which says send a PUT request adding
'_action=com.ibm.team.workitem.taskWorkflow.action.Complete' in the
end like below.

'https://localhost:9443/jazz/resource/itemOid/com.ibm.team.workitem.WorkItem/_0xazQG2dEd-Tlez1oMG4hw?_action=com.ibm.team.workitem.taskWorkflow.action.Complete

But it doesn't work.

I check that type is a Task which is using default task workflow , id
'com.ibm.team.workitem.taskWorkflow'.

Any hint for this?

The approach sounds correct, but you must also make sure that the work
item is in a state that actually allows the action.

I checked that work item in right status so it should be transitioned
with OSLC API request.
I check that workitem is a task and workflow definition like below.

workflowDefinition
action icon="processattachment:/workflow/inprogress.gif"
id="com.ibm.team.workitem.taskWorkflow.action.startWorking"
name="Start Working" state="s2"/
/workflowDefinition

So I sent a request like below but it still doesn't work.

https://localhost:9443/jazz/resource/itemOid/com.ibm.team.workitem.WorkItem/_0xazQG2dEd-Tlez1oMG4hw?_action=com.ibm.team.workitem.taskWorkflow.action.startWorking

I don't understand why.
Any idea?

Thank you so much for posting this. I just spent an hour first trying
to do a 'partial update' to the work item, then a full update, then
changing headers... ugh.

This is so easy -- it'd be nice if this sort of thing was documented
somewhere, like here:
http://open-services.net/bin/view/Main/CmRestApiV1