insert to table dropdown-list

<?php
header('Content-Type: text/html; charset=utf-8');
include("con.php"); //insert data server

try {
  // read from products table
  $sqlproducts = "SELECT product_name, product_number FROM products ORDER BY product_name ASC";
  $stmt1 = $pdo->prepare($sqlproducts);
  $stmt1->execute();
  $resultsproducts = $stmt1->fetchAll(PDO::FETCH_ASSOC);
  // read from suppliers table
  $sqlsuppliers = "SELECT supplier_name, ID FROM suppliers ORDER BY supplier_name ASC";
  $stmt2 = $pdo->prepare($sqlsuppliers);
  $stmt2->execute();
  $resultssupliers = $stmt2->fetchAll(PDO::FETCH_ASSOC);

  if($_SERVER['REQUEST_METHOD'] == 'POST') {
    $pdo->beginTransaction();
    $prodnumber = $_REQUEST["output"];
    $suppliernumber = $_REQUEST["output1"];
    $amount = $_POST['amount'];
    $project_number = 0;
    $amount_out = 0;
   /*
    echo "Prod:";
    echo $prodnumber;
    echo '<br>';
    echo "Supplier:";
    echo $suppliernumber;
    echo '<br>';
    echo "Amount:";
    echo $amount;
    echo '<br>';
   */
    if(empty($prodnumber) || empty($suppliernumber) || empty($amount)) {
    ?>
     <div id="dialog-message" title="שגיאה">
      <p align="right">
       <span class="ui-icon ui-icon-circle-close" style="float:right; margin:0 7px 50px 0;"></span>
        יש למלא את כל השדות
      </p>
     </div>
    <?php
    } else {
    $sql = "INSERT INTO inventory_stock (product_number, supplier_ID, project_number, amount_in, amount_out) VALUES (:product_number, :supplier_ID, :project_number, :amount_in, :amount_out)";
    $stmt = $pdo->prepare($sql);
    $stmt->execute(['product_number' => $prodnumber, 'supplier_ID' => $suppliernumber, 'project_number' => $project_number, 'amount_in' => $amount, 'amount_out' => $amount_out]);
    $pdo->commit();
    ?>
     <div id="dialog-message" title="הצלחה">
      <p align="right" >
       <span class="ui-icon ui-icon-circle-check" style="float:right; margin:0 7px 50px 0;"></span>
       נקלט בהצלחה
      </p>
     </div>
    <?php
    }
  }
  $prodnumber = "";
  $suppliernumber = "";
  $amount = "";
}

catch(Exception $e){
  $pdo->rollBack();
  ?>
  <div id="dialog-message" title="שגיאה">
   <p align="right">
    <span class="ui-icon ui-icon-circle-close" style="float:right; margin:0 7px 50px 0;"></span>
     שגיאה! לא נעשה עדכון
   </p>
  </div>
  <?php
  echo "<br>" . 'N° : '.$e->getCode();
  echo "<br>" . 'Error : '.$e->getMessage();
  $pdo = null;
}
?>

<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel = "stylesheet" type = "text/css" href = "myStyle.css"/>
    <link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
    <script src="https://code.jquery.com/jquery-1.12.4.js"></script>
    <script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
    <title>הכנסה למלאי</title>
    <style>
    .form-control {
     border: -1px solid #ccc;
     text-align: right;
    }
    </style>
</head>
<body>
 <form action="" method="POST" class="form-style-9">
 <div align="right">
     <H1 align="right">מלאי נכנס</H1>
  <ul>
    <li>
    <!-- שם מוצר ושמירת המק"ט -->
    <select class="field-style field-split align-left" name='productsnumber' onChange='outputValue(this)'>
    <option value='' selected disabled>בחר מוצר</option>
    <?php foreach($resultsproducts as $row)
    {
      echo "<option value='" . $row['product_number'] . "'>" . $row['product_name'] . "</option>";
    }?>
    </select>
    <input type='hidden' id='output' name='output' readonly />
    </li>

    <li>
    <!-- שם הספק -->
    <select class="field-style field-split align-right" name='suppliersnumber' onChange='outputValue1(this)'>
    <option value='' selected disabled>בחר שם הספק</option>
    <?php foreach($resultssupliers as $row)
    {
      echo "<option value='" . $row['ID'] . "'>" . $row['supplier_name'] . "</option>";
    }?>
    </select>
    <input type='hidden' id='output1' name='output1' readonly />

    <input type="number" name="amount" placeholder="הכנס כמות" class="field-style field-split align-left " />

    <li>
     <input type="submit" value="הכנס מלאי חדש" style = "font-size:20px; float:right">
    </li>
  </ul>
 </div>
 </form>
</body>
</html>
<script>
function outputValue(item)
{
 document.getElementById('output').value = item.value;
}
function outputValue1(item)
{
 document.getElementById('output1').value = item.value;
}

$( function(){
  $( "#dialog-message" ).dialog({
    modal: true,
    buttons: {
     Ok: function() {
      $( this ).dialog( "close" );
     }
    }
  });
});
</script>