嘿，我正在填写注册表，这是我的代码

if (isset($_POST['submit'])) {
    $GST = $_POST['GST'];
    $email = $_POST['email'];
     $contact = $_POST['contact'];
  $whatsapp = $_POST['whatsapp'];
     $adhaar = $_POST['adhaar'];
     $username = $_POST['username'];
     $password = $_POST['password'];
     $pan = $_POST['pan'];
     $district = $_POST['district'];
// Define variables and initialize with empty values



$sql = "SELECT email FROM users WHERE email = '$email'";
$result = mysqli_query($con,$sql);

if (mysqli_num_rows($result) == 1) {
    echo "string";
}else{
    $sql2 = "INSERT INTO users (username,password,email,district,gst,watsapp,adhaar,contact,pan) VALUES ($username,$password,$email,$district,$GST,$whatsapp,$adhaar,$contact,$pan)";

    if (mysqli_query($con,$sql2)) {
   $customername = $_POST['product_name'];
   foreach ($customername as $key => $value) {//start ho rah hai
       $sql = "INSERT INTO center (id) VAlues ('$value')";
       if (mysqli_query($con,$sql)) {
    echo "string";
}
   }// khatam ho rha hai ye 
}else{
 echo "Error: " . $sql . "<br>" . mysqli_error($con);
}

}



}

   ?>

并且我收到此错误错误：从用户那里选择电子邮件，电子邮件='dhruv@gmail.com'

如果我不使用此代码

$customername = $_POST['product_name'];
   foreach ($customername as $key => $value) {//start ho rah hai
       $sql = "INSERT INTO center (id) VAlues ('$value')";
       if (mysqli_query($con,$sql)) {
    echo "string";
}

然后它没有显示错误，我无法理解正在发生的事情。