In 99% of cases, seeing a blank page when clicking the PDF download link is due to your site still being password protected (showing a Coming Soon page).

As soon as you remove the password protection on your store then the links will work and create the PDF for you.

While you have password protection turned on, Shopify will block any and all links to your site, including the PDF links.

Note: If your store requires password protection to remain enabled, get in contact with our support team and they will provide you with a workaround.