Invoice Number in Filename

Hey there,

is there any possibility to get the formatted Invoice number into the filename?

I’ve tried:

add_filter( 'wpo_wcpdf_filename', 'wpo_wcpdf_custom_filename', 20, 4 );
function wpo_wcpdf_custom_filename( $filename, $template_type, $order_ids, $context ) {
	global $wpo_wcpdf;

	switch ($template_type) {
		case 'invoice':
			$count = $wpo_wcpdf->export->set_invoice_number( $order_id );
			$name = _n( 'Invoice_', 'Invoice_', $count, 'wpo_wcpdf' );
			$company = $wpo_wcpdf->export->order->shipping_company;
			$city = $wpo_wcpdf->export->order->shipping_city;
			$number = $wpo_wcpdf->export->get_display_number( $order_ids[0] );
			break;
		default:
			$name = $template_type;
			$company = $wpo_wcpdf->export->order->shipping_company;
			$city = $wpo_wcpdf->export->order->shipping_city;
			$number = $wpo_wcpdf->export->order->get_order_number();
			break;
	}

	if ( $count == 1 ) {
		$suffix = $number . '-' . $company .  $city;
	} else {
		$suffix = date('Y-m-d'); // 2020-11-11
	}

	$filename = $name . '-' . $suffix . '.pdf';

	return $filename;
}

but the Invoice number won’t shown up. Any ideas? Thx in advance!

https://wordpress.org/plugins/woocommerce-pdf-invoices-packing-slips/