Hello
Do you use Germanized Pro ?
Please, read the topic https://algolplus.freshdesk.com/support/solutions/articles/25000016635-add-calculated-field-for-order-
use metakey german_invoice_numbers and following code
thanks, Alex
add_filter('woe_get_order_value_german_invoice_numbers', function ($value,$order, $field) {
$invoices = wc_gzdp_get_invoices_by_order( $order );
if( $invoices ) {
$numbers = array();
foreach ( $invoices as $id => $invoice ) {
$numbers[] = $invoice->get_title();
}
$value = join(", ", $numbers);
}
return $value;
}, 10, 3);
Open section “Setup fields”, click “Add field”, select meta key _wcpdf_invoice_number , fill Column name, click “Confirm” and drag field to left column.