Getting ID via link

#1

How to get ID from link (From dynamically generated content) and get that ID onto the next page?
The product is linking to the product page where I will display the content there, but how do I pass that ID over?

<?php 		
$result = mysqli_query($con, "SELECT * FROM products");	
		  
while($row = mysqli_fetch_array($result)) {
?>					

    <div class="col-lg-3 col-md-6 mb-4">
      <div class="product align-items-left">
        <div class="view overlay productview">
          <img src="img/<?php echo $row['productimage']; ?>" class="img-top"
            alt="">
          <a>
            <div class="mask rgba"></div>
          </a>
        </div>
        <div class="cardtext">
          <a href="productpage.php?id=<?php echo $row['productID'];?>">
            <h3><?php echo $row['name']; ?></h3>
          </a>
			<h4><?php echo $row['price']; ?></h4>
			<h5><?php echo $row['gen']; ?></h5>
        </div>
      </div>
    </div>
<?php 
}
?>

Many thanks.

#2
if(!isset($_GET['id'])  {
    header('location: index.php');
    exit();
}
echo $_GET['id']