http.GET() response -2 but data are sent properly | ESP8266 Wi-Fi Module | Forum

I need to check data are correctly handled. Now I try to get httpcode and always returns -2 but data are sent properly. The code is:

if (client.connect("api.thingspeak.com",80)) {
writeAPIKey = "key=XXXXXXXXXXX";
tsfield1Name = "&field1=10";
request_string = thingSpeakAddress;
request_string += "key=";
request_string += "XXXXXXXXXXXX";
request_string += "&";
request_string += "field5";
request_string += "=";
request_string += (tempe);
http.begin(request_string);
http.GET();
int httpCode = http.GET();
Serial.println(httpCode);
String payload = http.getString(); //Get the request response payload
Serial.println(payload);
http.end();

I am sure something is wrong.