Error 500 when try make transition via rest

[aas]

Hello everybody. I try to make transition in another instance of Jira and have 500 error in response and also at that time have exception: 

org.apache.http.ConnectionClosedException: Premature end of chunk coded message body: closing chunk expected

def http = new HTTPBuilder("${addressJira}/rest/api/2/issue/${fieldValue}/transitions")
try {
      http.request(POST, ContentType.JSON) {
      requestContentType = ContentType.JSON
      request.addHeader("authorization: Basic ${authString}", "ContentType:        application/json")
        body = ["transition" : ["id": "11"]]

        response.success = { resp ->
            log.info("Successful " + resp.status.toString())
        }

        response.failure = { resp ->
            HttpResponseDecorator.HeadersDecorator headers = resp.getHeaders()
            for (Iterator i = headers.iterator(); i.hasNext();){
                def header = i.next()
                log.info(header)
            }
            log.warn("response is : " + resp.getData().toString())
        }
    }
} catch(Exception e){
    log.warn("Eception : " + e)
}

I tried to look at response like that 

resp.getEntity().getContent().getText()

and found out that :

java.lang.IllegalArgumentException: Input byte array has incorrect ending byte at 36

 Is it means that my request is wrong?

[aas]

If it interesting to somebody I found out the solution. 500 error was because of apache.

ConnectionClosedException was because of small time out 

The IllegalArgumentException problem was because of incorrect auth headers.

def authString = "${user}:${password}".bytes.encodeBase64().toString() 
try {
     http.request(POST, ContentType.JSON) {
     headers.'Authorization' = "Basic ${authString}"