How to request OAuth2 token to kong plugin

i am following this tutorial https://medium.com/@far3ns/kong-oauth-2-0-plugin-38faf938a468 and when i request the tokens with

Headers: Content-Type:application/jsonHost:api.ct.idBody:{“client_id”: “CLIENT_ID_11”,“client_secret”: “CLIENT_SECRET_11”,“grant_type”: “password”,“provision_key”: “kl3bUfe32WBcppmYFr1aZtXxzrBTL18l”,“authenticated_userid”: “oneone@gmail.com”,“scope”: “read”} 

it returns

{"error_description": "Invalid client authentication","error": "invalid_client"}

no matter what i tried i couldn't fix it, any idea how to make it work properly