从Swift发送HTTP post请求到数据库mysql

I am making a signup system( getting users information such as name, email) using Swift as a front end, php as a backend, and mysql as a database. ( using my own server, not localhost) and trying to send HTTP post request from Swift to insert data to user tables.(mySQL). I'm using a secure https url.

The problem is that when I try to pass data (firstname, last name, email, password), I always get a bad request (400) “Missing required information” like the screenshot and can’t let users to sign up… enter image description here

If i could pass the data, I should get the success response (200) “Registration successful”. The function inside the php is called so I assume there’s nothing wrong with my php code but the Swift code.

I want to know the reason why I cannot pass the data to my server(maybe from MySQL setting?). Thanks in advance and happy coding!

My php file(file name: registerUser.php):

<?php

  require("Conn.php");
  require("MySQLDAO.php");

  $returnValue = array();

  if(empty($_REQUEST["userEmail"]) || empty($_REQUEST["userPassword"]) || empty($_REQUEST["userFirstName"]) || empty($_REQUEST["userLastName"]))

  {

    $returnValue["status"]="400";
    $returnValue["message"]="Missing required information";
    echo json_encode($returnValue);
    return;
  }

  $userEmail = htmlentities($_REQUEST["userEmail"]);
  $userPassword = htmlentities($_REQUEST["userPassword"]);
  $userFirstName = htmlentities($_REQUEST["userFirstName"]);
  $userLastName = htmlentities($_REQUEST["userLastName"]);

  //generate secured passowrd 
  $salt = openssl_random_pseudo/bytes(16);
  $secured_password = sha1($userPassword . $salt);

  $dao = new MySQLDAO(Conn::$dbhost, Conn::$dbuser, Conn::$dbpassword, Conn::$dbname);
  $dao->openConnection();

  //check if user with provided username is available 
  $userDetails = $dao->getUserDetails($userEmail);
  if (!empty($userDetails))
  {
    $returnValue["status"]="400";
    $returnValue["message"]="Please choose a different email address";
    echo json_encode($returnValue);
    return; 

  }

  //Register new User 
  $result = $dao->registerUser($userEmail, $userFirstName, $userLastName, $secured_password, $salt);

  if($result){

    $userDetails = $dao->getUserDetails($userEmail);
    $returnValue["status"] = "200";
    $returnValue["message"] = "Registration successful";
    $returnValue["userId"] = $userDetails["user_id"];
    $returnValue["userFirstName"] = $userDetails["first_name"];
    $returnValue["userLastName"] = $userDetails["last_name"];
    $returnValue["userEmail"] = $userDetails["email"];

  } else {
      $returnValue["status"]="400";
      $returnValue["message"]="Couldn't register";

  }

$dao->closeConnection();

echo json_encode($returnValue);

?>

My Swift code:

 lazy var submitButton: UIButton = {
    let button = UIButton(type: .system)
    button.backgroundColor = UIColor(red:0.09, green:0.51, blue:0.92, alpha:1.0)
    button.translatesAutoresizingMaskIntoConstraints = false
    button.setTitle("Signup", for: .normal)
    button.setTitleColor(.white, for: .normal)
    button.addTarget(self, action: #selector(handleSubmit), for: .touchUpInside)
    return button

}()

func handleSubmit() {
    guard let userFirstName = userFirstNameTextField.text, let userLastName = userLastNameTextField.text, let userEmail = emailTextField.text, let userPassword = passwordTextField.text, let repeatPassword = repeatPasswordTextField.text

        else {
            print("Form is not valid")
            return
    }

    if (userPassword != repeatPassword) {
        self.displayAlertMessage(userMessage: "Passwords do not match")
        return
    }

    if (userFirstName.isEmpty || userLastName.isEmpty || userEmail.isEmpty || userPassword.isEmpty) {

        self.displayAlertMessage(userMessage: "All fields are required")
        return
    }

let myUrl = NSURL(string: "https://my URL name/registerUser.php")
let request = NSMutableURLRequest(url: myUrl! as URL)
request.httpMethod = "POST"
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
request.addValue("application/json", forHTTPHeaderField: "Accept")

let postString = "userEmail=\(userEmail)&userFirstName=\(userFirstName)&userLastName=\(userLastName)&userPassword=\(userPassword)"

request.httpBody = postString.data(using: String.Encoding.utf8)

let task = URLSession.shared.dataTask(with: request as URLRequest) {(data:Data?, response:URLResponse?, error: Error?) -> Void in

    DispatchQueue.main.async {

        if error != nil {
            self.displayAlertMessage(userMessage: "Error")
            return
        }

        do {

        let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary

        if let parseJSON = json {
            let userId = parseJSON["userId"] as? String

            if (userId != nil) {

            let myAlert = UIAlertController(title: "Success", message: "Registration Successful", preferredStyle: UIAlertControllerStyle.alert)
            let okAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil)
            myAlert.addAction(okAction)
                self.present(myAlert, animated: true, completion: nil)

        } else {

                print(123)
            let errorMessage = parseJSON["message"] as? String
                if (errorMessage  != nil) {

                self.displayAlertMessage(userMessage: errorMessage!)
                }
            }
        }

    } catch {
        print(error)

    }

    }

    }

    task.resume()
}