How do I apply asm policy using iControlREST?

I'm trying to change enforcementMode by using RESTAPI. But I can not apply-policy.

GET /mgmt/tm/asm/policies/js4y3P-sabtgiQOxWlU6Vg

{ ... "enforcementMode": "transparent", "isModified": false, ... }

PATCH /mgmt/tm/asm/policies/js4y3P-sabtgiQOxWlU6Vg

{ "enforcementMode": "blocking" }

GET /mgmt/tm/asm/policies/js4y3P-sabtgiQOxWlU6Vg

{ ... "enforcementMode": "blocking", "isModified": true, ... }

POST /mgmt/tm/asm/tasks/apply-policy/js4y3P-sabtgiQOxWlU6Vg (body is empty)

{ ... "code": 400, "message": "request.body", ... }

POST /mgmt/tm/asm/tasks/apply-policy/js4y3P-sabtgiQOxWlU6Vg (body is '{}')

{ ... "code": 404, "message": "Could not get the Apply Policy Task, No matching record was found.", ... }

Thanks in Advance.