massivegeek

I managed to get this working in the end, if anyone else stumbles across this the following code worked.

function invoice_custom_order_fields( $fields, $order ) {
    $new_fields = array();
        
    if( get_post_meta( $order->id, '_barcode_image', true ) ) {
        $new_fields['Barcode'] = array( 
            'label' => 'Order Barcode',
      'value' => '<img src="/?wc_barcode='.get_post_meta( $order->id, '_barcode_text', true ).'" width="200" height="40" />'
        );
    }
    
    return array_merge( $fields, $new_fields );
}
add_filter( 'wcdn_order_info_fields', 'invoice_custom_order_fields', 10, 2 );