Множественный выбор и добавление дополнительных полей не работает

Я впервые использую несколько вариантов выбора и добавляю больше функций поля в форму. У меня есть эта форма, где я могу ввести несколько serialNumber, а также добавить несколько аксессуаров и количество соответственно. Но только первый выбранный серийный номер и аксессуары (и количество) сохранены в моей базе данных.

Итак, вот моя форма HTML:

<form id="form1" name="form1" method="post" action="requisitionForm_process.php" onsubmit="return validateForm()" >
<div class="form-group">
<label for="DONO">DO. Number: </label>
<input class="form-control" id="DONO" name="DONO" placeholder="Place DO. Number Here" type="text"/>
</div>
<div class="form-group">
<label for="requestby">Request By: </label>
<select class="form-control" id="empCode" name="empCode">
<?php while ($row = mysqli_fetch_array($resultR)):;?>
<option value = <?php echo $row ['empCode']; ?>><?php echo $row ['empCode']; echo ":"; echo $row ['empName'];?></option>
<?php endwhile;
?>
</select>
</div>
<div class="form-group">
<label for="requestby">Customer: </label>
<select class="form-control" id="customerCode" name="customerCode">
<?php while ($row = mysqli_fetch_array($resultC)):;?>
<option value = <?php echo $row ['customerCode']; ?>><?php echo $row ['customerCode']; echo ":"; echo $row ['customerName'];?></option>
<?php endwhile;
?>
</select>
</div>
<div class="form-group"> <!-- Date input -->
<label class="control-label" for="dateOUT">Date:</label>
<input class="form-control" id="dateOUT" name="dateOUT" placeholder="DD/MM/YYY" type="text"/>
</div>
<div class="form-group">
<label for="categoryCode">Category: </label>
<select class="form-control" id="categoryCode" name="categoryCode">
<option value="new"> New Installation</option>
<option value="re">Re-installation</option>
</select>
</div>
<div class="form-group">
<label for="categoryCode">Product: </label>
<select class="form-control" id="productCode" name="productCode">
<?php while ($row = mysqli_fetch_array($result)):;?>
<option value = <?php echo $row ['productCode']; ?>><?php echo $row ['productCode']; echo ":"; echo $row ['productName'];?></option>
<?php endwhile;
?>
</select>
</div>
<div class="form-group">
<label for="serialNumber">Serial Number:</label><br>
<select id="serialNumber" name="serialNumber[]" multiple class="form-control" >
<?php while ($row = mysqli_fetch_array($resultSe)):;?>
<option value = <?php echo $row ['serialNumber']; ?>><?php echo $row ['serialNumber'];?></option>
<?php endwhile;?>
</select>
</div>
<table class="table table-bordered" id="item_table">
<tr>
<th>Select Accessories</th>
<th>Enter Quantity</th>
<th><button type="button" name="add" class="btn btn-success btn-sm add"><span class="glyphicon glyphicon-plus"></span></button></th>
</tr>
</table>
<div class="form-group">
<input type="button" class="btn"  id="checkBtn" name="return" value="Back" onClick="javascript: window.history.back(-1)";>
<input class="btn btn-primary" type="reset" value="Reset">
<input align="right" type="submit" class="btn btn-info" value="Submit Button">
</div>
</div>
</form>

И это мой процесс PHP:

<?php

if(isset($_POST["serialNumber"]))
{
$serialNumber = '';
foreach($_POST["serialNumber"] as $row)
{
$serialNumber .= $row . ', ';
}
$serialNumber = substr($serialNumber, 0, -2);


if(isset($_POST["categoryCode"]))
{
$connect = new PDO("mysql:host=localhost;dbname=ims", "root", "");
$DONO = $_POST["DONO"];
$empCode = $_POST["empCode"];
$customerCode = $_POST["customerCode"];
$categoryCode = $_POST["categoryCode"];
$productCode = $_POST["productCode"];
$dateOUT = date('Y-m-d', strtotime($_POST['dateOUT']));
for($count = 0; $count < count($_POST["accID"]); $count++)
{
$query = "INSERT INTO requisition (DONO, empCode, customerCode, dateOUT, categoryCode, productCode, serialNumber, quantityAcc, accID) VALUES (:DONO, :empCode, :customerCode, :dateOUT, :categoryCode, :productCode, :serialNumber, :quantityAcc, :accID) ";
$statement = $connect->prepare($query);
$statement->execute(
array(
':DONO'   => $DONO,
':empCode'   => $empCode,
':customerCode'   => $customerCode,
':dateOUT'   => $dateOUT,
':categoryCode'   => $categoryCode,
':productCode'   => $productCode,
':serialNumber'   => $serialNumber,
':quantityAcc' => $_POST["quantityAcc"][$count],
':accID'  => $_POST["accID"][$count]
)
);
}
$result = $statement->fetchAll();
if(isset($result))
{
echo 'ok';
}
}
}

?>