Not make post request

1

Hi, the kotlin code does a rest call to the backend but when I run the code I have an error on the urlConnection.connect () line, the error is the code below, how do I fix this?
Error:
android.os.NetworkOnMainThreadException
2021-05-07 16:01:18.792 24813-24813/com.app.xx W/System.err: at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1605)
2021-05-07 16:01:18.792 24813-24813/com.app.xx W/System.err: at java.net.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:115)
2021-05-07 16:01:18.792 24813-24813/com.app.xx W/System.err: at java.net.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:103)
2021-05-07 16:01:18.792 24813-24813/com.app.xx W/System.err: at jav

Code:
fun getToken(ID_AUTH_FIREBASE:String,UTENTE:String,ADMIN_KEY:String ): String {
val dta = StringBuilder()

        try {
            // Creating & connection Connection with url and required Header.
            val url = URL("http://url")
            val urlConnection: HttpsURLConnection = url.openConnection() as HttpsURLConnection
            urlConnection.setRequestProperty("Content-Type", "application/json")
            urlConnection.requestMethod = "POST" //POST or GET
            urlConnection.connect()

            // Create JSONObject Request
            val jsonRequest = JSONObject()
            jsonRequest.put("ID_AUTH_FIREBASE", ID_AUTH_FIREBASE)
            jsonRequest.put("UTENTE", UTENTE)
            jsonRequest.put("ADMIN_KEY", ADMIN_KEY)

            // Write Request to output stream to server.
            val out = OutputStreamWriter(urlConnection.getOutputStream())
            out.write(jsonRequest.toString())
            out.close()


            // Check the connection status.
            val statusCode: Int = urlConnection.getResponseCode()
            val statusMsg: String = urlConnection.getResponseMessage()

            // Connection success. Proceed to fetch the response.
            if (statusCode == 200) {
                val it: InputStream = BufferedInputStream(urlConnection.getInputStream())
                val read = InputStreamReader(it)
                val buff = BufferedReader(read)

                var chunks: String=""
                while (buff.readLine().also({ chunks = it }) != null) {
                    dta.append(chunks)
                }
                System.out.println("Valore: "+dta.toString())
                return dta.toString()
            } else {
                //Handle else case
            }
        } catch (e: Exception) {
            System.out.println("Errore: "+e)
            System.out.println(e.printStackTrace())
        }

      return dta.toString()
    }