//Payload
{"StatusSNS":{"Time":"2018-05-26T16:29:48","DS18B20":{"Temperature":24.8},"TempUnit":"C"}}

//Code

HTTPClient http;    //Declare object of class HTTPClient

  //GET Data
  String Link = "http://192.168.1.59/cm?user=admin&password=pass&cmnd=status%2010";

  http.begin(Link);     //Specify request destination

  int httpCode = http.GET();            //Send the request
  String payload = http.getString();    //Get the response payload

  //Serial.println(httpCode);   //Print HTTP return code
  //Serial.println("Payload: " + payload);    //Print request response payload

  //Start- und Endposition des Substring für die Temperatur
  int posStart = payload.indexOf("re:") + 3;
  int posEnd = payload.indexOf("},T");

  Serial.println("posStart: " + posStart);
  Serial.println("posEnd: " + posEnd);

//Serial Output
sStart:
<empty line>