Bulldogbob on Bad request 400

Hello , i use a WeMos D1 mini with a BME280 on my channel . It has worked with this sketch , but now i get bad request 400 . What went wrong ?? 

#include <BME280_MOD-1022.h>
#include <Wire.h>

// Wifi and ThingSpeak settings
#include <ESP8266WiFi.h>

const char* ssid = "XXXXXX";
const char* password = "XXXXXXXXX";

const char* server = "api.thingspeak.com";
const char* api_key = "DFFSB76BCWGXXXX";

// Measurement interval (seconds)
const int interval = 300; //5 mins

#define LED D4

WiFiClient client;

void printFormattedFloat(float x, uint8_t precision) {
char buffer[10];

dtostrf(x, 7, precision, buffer);
Serial.print(buffer);

}

void printCompensatedMeasurements(void) {

float temp, humidity, pressure, pressureMoreAccurate;
double tempMostAccurate, humidityMostAccurate, pressureMostAccurate;
char buffer[80];

temp = BME280.getTemperature();
humidity = BME280.getHumidity();
pressure = BME280.getPressure();

pressureMoreAccurate = BME280.getPressureMoreAccurate(); // t_fine already calculated from getTemperaure() above

tempMostAccurate = BME280.getTemperatureMostAccurate();
humidityMostAccurate = BME280.getHumidityMostAccurate();
pressureMostAccurate = BME280.getPressureMostAccurate();

Serial.print("Temperature: ");
printFormattedFloat(tempMostAccurate, 2);
Serial.println();

Serial.print("Humidity: ");
printFormattedFloat(humidityMostAccurate, 2);
Serial.println();

Serial.print("Pressure: ");
printFormattedFloat(pressureMostAccurate, 2);
Serial.println();

// Post data to ThingSpeak
postData(tempMostAccurate, humidityMostAccurate, pressureMostAccurate);
Serial.println();
}

void postData(float temperature, float humidity, float pressure){
// Send data to ThingSpeak
if (client.connect(server,80)) {
Serial.println("Connect to ThingSpeak - OK");

String dataToThingSpeak = "";
dataToThingSpeak+="GET /update?api_key=";
dataToThingSpeak+=api_key;

dataToThingSpeak+="&field1=";
dataToThingSpeak+=String(temperature);

dataToThingSpeak+="&field2=";
dataToThingSpeak+=String(humidity);

dataToThingSpeak+="&field3=";
dataToThingSpeak+=String(pressure);

dataToThingSpeak+=" HTTP/1.1
Host: a.c.d
Connection: close

";
dataToThingSpeak+="";
client.print(dataToThingSpeak);

int timeout = millis() + 5000;
while (client.available() == 0) {
if (timeout - millis() < 0) {
Serial.println("Error: Client Timeout!");
client.stop();
return;
}
}
}
while(client.available()){
String line = client.readStringUntil('
');
Serial.print(line);
}
}

// Setup wire and serial
void setup()
{
Wire.begin();
Serial.begin(115200);
pinMode(LED, OUTPUT);
delay(10);
Serial.println("Connecting to wifi...");
WiFi.begin(ssid, password);

while (WiFi.status() != WL_CONNECTED){

// Blink LED when connecting to wifi
digitalWrite(LED, LOW);
delay(250);
digitalWrite(LED, HIGH);
delay(250);
}
Serial.println("WiFi connected");

// Prepare LED to turn on when measuring and send data

}

// main loop
void loop()
{
// need to read the NVM compensation parameters
BME280.readCompensationParams();

// We'll switch into normal mode for regular automatic samples
BME280.writeStandbyTime(tsb_0p5ms); // tsb = 0.5ms
BME280.writeFilterCoefficient(fc_16); // IIR Filter coefficient 16
BME280.writeOversamplingPressure(os16x); // pressure x16
BME280.writeOversamplingTemperature(os2x); // temperature x2
BME280.writeOversamplingHumidity(os1x); // humidity x1

BME280.writeMode(smNormal);

while (1) {
//digitalWrite(LED, LOW);
while (BME280.isMeasuring()) {
//Serial.println("Measuring...");
//delay(100);
}

// read out the data - must do this before calling the getxxxxx routines
BME280.readMeasurements();
printCompensatedMeasurements();
// digitalWrite(LED, HIGH);

delay(interval*1000);
Serial.println();
}
}