"Invalid Order" error when generating second custom PDF template

Question

I’m using the WooCommerce PDF Invoices & Packing Slips plugin by WP Overnight.

I’ve successfully:

• Created a second custom PDF template (a voucher version without prices).
• Added a button on the Thank You page to download that second template.

Everything appears to be set up correctly — but when I click the new button, I get this error:

Invalid Order The order ID being passed is correct (I double-checked the value and it matches the order that just completed).

What I’ve done:

Created the second template under my child theme: wp-content/themes/child-theme/woocommerce/pdf/voucher.php And registered it via filter adding a custom button on Thank you page:

add_action('woocommerce_thankyou', 'add_voucher_pdf_button', 20);
function add_voucher_pdf_button($order_id) {
 if (!$order_id) return;
 
 $order = wc_get_order($order_id);
 if (!$order) return;
 // Nonce for security, must match the document type (invoice)
 $nonce = wp_create_nonce('generate_wpo_wcpdf');
 
 // Build the correct AJAX URL
 $pdf_url = add_query_arg(array(
 'action' => 'generate_wpo_wcpdf',
 'document' => 'invoice', // keep as invoice, since voucher isn’t a registered type
 'order_ids' => $order->get_id(),
 'voucher_pdf' => 1,
 '_wpnonce' => $nonce,
 ), admin_url('admin-ajax.php'));
 
 echo '<a href="' . esc_url($pdf_url) . '" target="_blank" class="button alt" style="margin-top:20px;">Download Voucher PDF</a>';
}
add_filter('wpo_wcpdf_template_file', 'load_voucher_template_conditionally', 10, 3);
function load_voucher_template_conditionally($template, $type, $order) {
 if (!empty($_GET['voucher_pdf']) && $_GET['voucher_pdf'] == 1) {
 $voucher_template = get_stylesheet_directory() . '/woocommerce/pdf/voucher-template/' . basename($template);
 
 if (file_exists($voucher_template)) {
 return $voucher_template;
 }
 }
 return $template;
}

Any insight or example on how to do this correctly?

Answer 1

First you need to register your custom PDF type with WP Overnight so it’s a valid document:

add_filter( 'wpo_wcpdf_document_types', function( $document_types ) {
 $document_types['voucher'] = array(
 'title' => __( 'Voucher', 'your-textdomain' ),
 'description' => __( 'Custom voucher PDF without prices', 'your-textdomain' ),
 'template' => 'voucher.php',
 'folder' => 'woocommerce/pdf',
 'filename' => 'voucher-{order_number}.pdf',
 'attach_to_email' => false,
 'paper_size' => 'A4',
 );
 return $document_types;
});

Next, your button should pass the new document type:

add_action('woocommerce_thankyou', 'add_voucher_pdf_button', 20);
function add_voucher_pdf_button($order_id) {
 if (!$order_id) return;
 $order = wc_get_order($order_id);
 if (!$order) return;
 $nonce = wp_create_nonce('generate_wpo_wcpdf');
 $pdf_url = add_query_arg(array(
 'action' => 'generate_wpo_wcpdf',
 'document' => 'voucher', // <-- new document type
 'order_ids' => $order->get_id(),
 '_wpnonce' => $nonce,
 ), admin_url('admin-ajax.php'));
 echo '<a href="' . esc_url($pdf_url) . '" target="_blank" class="button alt" style="margin-top:20px;">Download Voucher PDF</a>';
}

Finally, place your template file here:

wp-content/themes/your-child-theme/woocommerce/pdf/voucher.php

Hope it works for you!