Mohon koreksi kesalahan syntax di code berikut

<?php
  require 'connection.php';
  checkLoginAtLogin();

  if (isset($_POST['btnLogin'])) {
  	$username = htmlspecialchars($_POST['username']);
  	$password = htmlspecialchars($_POST['password']);

  	$checkUsername = mysqli_query($conn, "SELECT * FROM user WHERE username = '$username'");
  	if ($data = mysqli_fetch_assoc($checkUsername)) {
  		if (password_verify($password, $data['password'])) {
  			$_SESSION = [
  				'id_user' => $data['id_user'],
  				'username' => $data['username'],
  				'id_jabatan' => $data['id_jabatan']
  			];
  			header("Location: index.php");
  		} else {
			setAlert("Password your insert is false!", "Check your Password BACK!", "error");
			header("Location: login.php");
	  	}
  	} else {
		setAlert("Username is not registered!", "Check your Username BACK!", "error");
		header("Location: login.php");
  	}
  }
?>