HTTP Task POST to login endpoint Bad Request - problem with body process variable

Flowable Engine
1

I’m trying to do a POST request using Http Task, but ResponseReason is “Bad Request”, so it must be some problem with the body I think, but I don’t know what is.
In my HTTP Task in the UI modeler I’ve set this:

image

and in XML file I have this:

 <flowable:field name="requestBody">
          <flowable:expression><![CDATA[${body}]]></flowable:expression>
        </flowable:field>

and in my application I’m passing the params this way (in Java):

@PostMapping(path = PathConstants.START_ACTION)
public ResponseEntity<BaseResponse<ProcessInstance>> start(@PathVariable String processDefinitionId,
		@RequestBody(required = false) Map<String, Object> params)

where params is (testing it in postman):

{
    "input":3,
    "body": {
    	"email":"peter@klaven", 
    	"password":"cityslicka" 
    }
}

and then runtimeService.startProcessInstanceById(processDefinitionId, params); so I’m expecting that the body variable is read correctly.
For further checking I’ve tried printing the body variable after starting process instance, and in fact I have this:

body={email=peter@klaven, password=cityslicka}

The error is saying that probably the body is malformed, right? So what am I doing wrong in passing/setting process variables?

EDIT

I’ve tried adding manually the body to the params Map this way:

params.put("body","{\"email\":\"peter@klaven\", \"password\":\"cityslicka\"}");

but the error is the same.