adding download invoice link in the google calendar order details page

gistfile1.txt

add_filter('pi_dtt_google_calendar_event_desc', function($desc, $order){

	$order_id = $order->get_id();

    $download_url = add_query_arg(
        array(
            'action'        => 'generate_wpo_wcpdf',
            'document_type' => 'invoice',
            'order_ids'     => $order_id,
            '_wpnonce'      => wp_create_nonce( 'generate_wpo_wcpdf' ),
        ),
        admin_url( 'admin-ajax.php' )
    );

	$desc .= '<br><br>';
	$desc .= '<a href="' . esc_url( $download_url ) . '" target="_blank">' . __( 'Download Invoice', 'woocommerce-pdf-invoices-packing-slips' ) . '</a>';
	$desc .= '<br><br>';
	
	return $desc;
}, 10, 2);