JSON post request being weird

[Seijboldt]

You are missing the content-length header. It is also advisable to use json.encode to create JSON strings instead of manual creation which can lead to errors.

I've added the header, with it in I get a internal server error  

This should be correct, right?

Code:

mac = io.readfile('/sys/class/net/eth0/address'):trim()
require('socket.http')
require('json')
require("ltn12")
jsoncontent = json.encode({fault = true,instID= "teststring",value= 22,name = "stringname"})

body = jsoncontent
response = {}
log("test")

socket.http.request({
      url = "http://192.168.1.69/docs",
   method = 'POST',
     sink = ltn12.sink.table(response),
  headers = {
     ["Content-Length"] = string.len(body),
        ['accept'] = 'application/json',
     ['content-type'] = 'application/json',
            },
      source = ltn12.source.string(body),
        })
log(response,body)