Gagal input ke database dan tidak muncul pesan error

tolong bantu gan saya coba input ke database pakai metode $_POST tapi gagal dan tidak muncul pesan error, sdh coba cari kesalahan tapi tidak ketemu

ini kode nya

<?php

$koneksi = new mysqli ("localhost", "root","","db_mk");

?>

<div class="row clearfix">
<div class="col-lg-12 col-md-12 col-sm-12 col-xs-12">
      <div class="card">
      <div class="header">
      <h2>Tambah Barang</h2>
</div>

<div class="body">

<form method="POST">

<label for="">Kode Barcode</label>
<div class="form-group">
    <div class="form-line">
<input type="number" name= "kode_barcode" class="form-control"  />
</div>
</div>

<label for="">Line</label>

<div class="form-group">
<div class="form-line">
<input type="text" name= "line" class="form-control"  />
</div>
</div>

<label for="">Style Name</label>
<div class="form-group">
<div class="form-line">
<input type="text" name= "style_name" class="form-control"  />
</div>
</div>

<label for="">Style Number</label>
<div class="form-group">
<div class="form-line">
<input type="text" name= "style_no" class="form-control"  />
</div>
</div>

<label for="">Color</label>
<div class="form-group">
<div class="form-line">
<input type="text" name= "color" class="form-control"  />
</div>
</div>
<label for="">Jumlah</label>

<div class="form-group">
<div class="form-line">
<input type="number" name= "jumlah" class="form-control"  />
</div>
</div>

<input type="submit" name="simpan" value="Simpan" class="btn btn-primary">

</form>
<?php

if(isset($_POST['simpan'])) {

$kode = $_POST['kode_barcode'];
$line = $_POST['line'];
$style_name = $_POST['style_name'];
$style_no= $_POST['style_no'];
$color= $_POST['color'];
$jumlah = $_POST['jumlah'];

$sql = $koneksi->query("insert into tb_barang values('$kode','$line','$style_name','$style_no','$color','$jumlah'");

if ($sql){
?>

<script type="text/javascript">
alert("Data Berhasil Disimpan");

</script>
<?php
 }

}
?>