Bagaimana cara mengunakan mysqli_insert_id?

Saya memiliki tabel booking yang berelasi dengan tabel detail_booking.

saya baca di beberapa artikel, agar kedua tabel mealkukan proses secara bersamaan menggunakan mysql_insert_id. ketika saya coba, id di tabel booking bernilai 0 di tabel detail_booking

code yang sayang masukan seperti ini

<?php
include '../config/connection.php';

$id_user = $_POST['id_user'];
$kd_paket = $_POST['kd_paket'];
$jml_org = $_POST['jml_org'];
$tgl_wisata = $_POST['tgl_wisata'];
$total_bayar = $_POST['total_bayar'];


$pack = mysqli_query($conn,"SELECT harga FROM paket WHERE kd_paket='$kd_paket'");
$data = mysqli_fetch_array($pack);
$total_bayar = $data['harga'] * $jml_org;

$sql = "INSERT INTO booking (id_user,kd_paket,jml_org,tgl_wisata) VALUES ('$id_user','$kd_paket','$jml_org','$tgl_wisata')";
$query = mysqli_query($conn,$sql);

$kd_booking = mysqli_insert_id();

	$book = "INSERT INTO detail_booking (kd_booking,total_bayar) VALUES ('".$kd_booking."','$total_bayar')";
	$ok = mysqli_query($conn,$book);
	if ($ok) {
		header('location:../mybooking.php');
	} else{
	    header('location:../profil-desa.php');
}
?>

mohon bantuannya, dimanakah letak kesalahan saya?

terima kasih