I am using mPDF along with the mpdf/qrcode library to generate QR codes and embed them in PDF documents. These PDFs are generated from data extracted from XLS files using PHPSpreadsheet. The entire process of reading the XLS files and generating the PDFs works correctly, with the exception of displaying the QR code. Despite generating what appears to be a valid QR code image, it does not display in the final PDF. The PDF is generated with no errors reported by mPDF, but the area where the QR code should be appears blank.