<form action="<?= site_url('Buyer_Controller/view_cart') ?>" method= "post">

    <div class="lalign">
      <input type="checkbox" /> <span id="normal-p" name="coupon" value="sku_<?php echo html_escape($p_item2['CouponID']) ?>">;
</div>
<button type="submit">Add to Cart</button>
</form>

public function view_cart()
    {

            $this->load->model("cart_model", "cartm");
            if (!empty($_SESSION['id']))
                redirect('Buyer_Controller');

               if(!isset($_POST['coupon'])) {

               redirect('Buyer_Controller/test');
               }

               else{

               $data= $_POST['coupon'];
               }

}