Embedded fonts in Apple Books not showing

I have all my fonts in the right folder, the CSS is fine, and the manifest references.

The ePUB displays with the correct embedded fonts in Calibre.

But in Apple Books, it defaults to some serif font, even though 'Original' is checked in the font menu.

I have <meta property="ibooks:specified-fonts">true</meta> in the .opf (not longer need a separate xml file).

So that seems to suggest that Apple Books cannot see the fonts being referenced. But other readers can.

Am I missing something?