Cannot get QR code to work at all

Have been using this PDF Builder for two years creating all manner of documents. Now I want to add a QR code for URL which is stored in an order meta field. I can’t get it to work at all.

I can create the custom field with the meta field value and set it to ‘QR’, then add it to PDF template, OR retrieve the meta field value as ‘simple text’ and in the PDF builder retrieve that via QR code field option.

Both result in: “There has been a critical error on this website.” when I generate the PDF from an order.

I can see that in the PHP Error log errors are being generated but can’t figure out what these mean.

Any help welcome.