add_filter( 'fakturownia/invoice_without_vat/data', 'wpdesk_fakturownia_add_transaction_id', 10, 2 );
function wpdesk_fakturownia_add_transaction_id( array $data, WPDesk\WooCommerceFakturownia\Data\DocumentData $document_data ) {
	foreach($data['positions'] as $key => $position){
		$data['positions'][$key]['tax'] = 'zw';
	}
	return $data;
}