Add WooCommerce coupon code automatically based on product categories

I am trying to add a coupon code automatically if the cart has products from specific categories. The price must be updated in the Total after showing the discount amount.

But I cant see any changes in the total, kindly help me.

My code:

add_action('wc_cart_product_subtotal' , 'getsubtotalc');
function getsubtotalc ($product_subtotal, $_product, $quantity, $object) {
    if( is_cart() || is_checkout() ) {
        global $woocommerce, $product;
        global $total_qty;
        /*$coupon_code = 'drawer';
        if ( $woocommerce->cart->has_discount( $coupon_code ) ) return;*/

        foreach ( $woocommerce->cart->cart_contents as $product ) {
            if( has_term( array('t-shirts-d','socks-d','joggers-d','boxers-d'), 'product_cat', $cart_item['product_id'] ) ){
                $coupon_code = 'drawer';
                if (!$woocommerce->cart->add_discount( sanitize_text_field( $coupon_code))) {
                    $woocommerce->show_messages();
                }
                echo '<div class="woocommerce_message"><strong>The number of Product in your order is greater than 10 so a 10% Discount has been Applied!</strong>
 </div>';
            }
        }
    }
}

Thanks