Blank PDF when created programmatically

Hi there,

Awesome plugin! I am trying to send all customers a PDF in the evening on the day of delivery.

The problem is that when I create a PDF it is blank. The PDF file has a size 107 KB but is completely blank when opened.

My code:

$pdfinvoice = new WooCommerce_PDF_Invoices_Export;
 $template_type= 'invoice';
$order_ids = array(140);
 $filename = 'theinvoice.pdf';

$dompdf =  $pdfinvoice->generate_pdf( $template_type, $order_ids );
$output = $dompdf->output();
file_put_contents($filename, $output);

WP_Debug shows no errors 🙁

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