Http_poller Web post request

I'm using http_poller to use POST request. It is giving error with the body.

I added body as below:

body => '{ "grant_type":"client_credentials","scope":"domain" }'

Error I'm seeing after running it as Bad request: 400

"message" => "Parameter conditions "grant_type" not met for actual request parameters: { "grant_type":"client_credentials","scope":"domain" }={}",

Please suggest corrections.