Code snippet to show next order coupon while printing invoice using "WooCommerce Print Invoice & Delivery Note"

support_print_invice_for_retainful.php

/*
* 1. wcdn_after_branding => After the invoice logo
* 2. wcdn_after_addresses => After displaying the billing and shipping address
* 3. wcdn_after_info => After order details
* 4. wcdn_after_items => After the order items table
* 5. wcdn_after_notes => After the order notes
* 6. wcdn_after_thanks => After thanks
* 7. wcdn_after_colophon => After colophon
*
* Replace `wcdn_after_addresses` with any other mentioned hooks to change the display position
*/

add_action('wcdn_after_addresses',function($order){
	do_action('rnoc_show_order_coupon',$order,true,'','');
});