Using groovy to promote a planning unit - syntax

We are building a groovy rule that will allow users to promote a planning unit.

However, our json response and body is returning

201

{"links":null,"type":"HP"}

Do we have syntax issue?

We've compared to the documented example, but we are not able to identify any differences

body='actionID=6&pmMembers="Entity1: Project1"&comments="promoting"'

    println("HardCoded body:\n$body") 

    HttpResponse<String> jsonResponse = connection.post("/planningunits/OEP_Plan::OEP_Working/actions")

     .header("Content-type", "application/x-www-form-urlencoded")

     .body(body)

     .asString();

      println (jsonResponse.status);

	  println (jsonResponse.body);