You can easily set "header" data in invoice using setInvoiceHeader function or You can set header data directly by passing array using setInvoiceHeaderData() function with "header" parameter. "Header" data normally includes "no", "date", "duedate", "total_due" etc. You can add or remove these fields.
$xinvoice = new Xinvoice(); //set header array $header = array("no" => "Nx-1001"); //set header data $xinvoice->setInvoiceHeaderData($header); echo $xinvoice->render();