i want to send data form my Esp8266 to an API PHP webside and then i got the error 400 from the Response Code

I’m trying to do a http request with my esp8266 and I get the Response code 400 from my ESP. Do you have an idea what is wrong with my code?

I used the Code from this Webside:
https://randomnerdtutorials.com/esp32-esp8266-mysql-database-php/

The Website is hosted by Strato

C code:

#include <ESP8266HTTPClient.h>
#include <WiFiClient.h>
#include <Wire.h>
#include <Adafruit_Sensor.h>

const char* ssid     = "----";
const char* password = "----";
const char* serverName = "----";
String apiKeyValue = "tPmAT5Ab3j7F9";

void setup() {

Serial.begin(115200);

  WiFi.begin(ssid, password);
  while(WiFi.status() != WL_CONNECTED) { 
    delay(500);
  }
    Serial.println("");
  Serial.print("Connected to WiFi network with IP Address: ");
  Serial.println(WiFi.localIP());
}

void loop() {
   
if(WiFi.status()== WL_CONNECTED){
    WiFiClient client;
    HTTPClient http;
    
    http.begin(client, serverName);
    http.addHeader("Content-Type", "application/x-www-form-urlencoded");

    String httpRequestData = "api_key=" + apiKeyValue
                          + "&sensor=" + '1'
                          + "&location=" + '2' 
                          + "&value1=" + '3'
                          + "&value2=" + '4' + "";
  Serial.println(httpRequestData);
    int httpResponseCode = http.POST(httpRequestData);
        if (httpResponseCode>0) {
      Serial.print("HTTP Response code: ");

      Serial.println(httpResponseCode);
    }
    else {
      Serial.print("Error code: ");
      Serial.println(httpResponseCode);
    }
    
    http.end();
  }
  else {
  }
  
  delay(10000);
}

PHP code:

$servername = '----';

$dbname = '----';
$username = '----';
$password = '----';
$Zeit = 'date("YmdHis")';

$api_key_value = "tPmAT5Ab3j7F9";

$api_key= $sensor = $location = $value1 = $value2 = $value3 = "";

if ($_SERVER["REQUEST_METHOD"] === "POST") {

    $api_key = test_input($_POST["api_key"]);

    if($api_key == $api_key_value) {
        $sensor = test_input($_POST["sensor"]);
        $location = test_input($_POST["location"]);
        $value1 = test_input($_POST["value1"]);
        $value2 = test_input($_POST["value2"]);
        
        $conn = new mysqli($servername, $username, $password, $dbname);

        if ($conn->connect_error) {
            die("Connection failed: " . $conn->connect_error);
        } 
        
        $sql = "INSERT INTO geraet_1 (sensor,Ort,Temperatur,Luftfeuchtigkeit,Zeit)
        VALUES (
            '" . $sensor . "',
            '" . $location . "',
            '" . $value1 . "',
            '" . $value2 . "',
            '" . $Zeit . "')";
        
        if ($conn->query($sql) === TRUE) {
            echo "New record created successfully";
        } 
        else {
            echo "Error: " . $sql . "<br>" . $conn->error;
        }
    
        $conn->close();
    }
    else {
        echo "Wrong API Key provided.";
    }
}
else {
    echo "No data posted with HTTP POST.";
}

function test_input($data) {
    $data = trim($data);
    $data = stripslashes($data);
    $data = htmlspecialchars($data);
    return $data;
} 

and here is the output from my esp:

HTTP Response code: 400

api_key=tPmAT5Ab3j7F9&sensor=1&location=1&value1=2&value2=5