The quote PDF is empty, why?

This issue may be due to your hosting using an outdated version of PHP.

You can check the version used by your hosting by going to "Advanced Settings / Info".

In the "Information about your server" section, you can see the PHP version number.

You can also ask this information directly to your hosting provider.

If the PHP version used on your server is less than 5.6, it must be updated.

Simply ask your hosting provider to do it.