KWGT unable to use TTF fonts

Using KWGT Pro ver 3.76b422110, on a Google Pixel 9 running Android 15.

TTF fonts are completely unusable in the app, with error message “Unable to read ext:/fonts/(font name).ttf”. Clearing cache does not help. The fonts are usable, as I’ve been able to install them to my PC with zero issues.
If it matters, I downloaded my fonts from FontStruct.

Are they in the Kustom/fonts folder?

Yes they are. In the font picker, they appear to be loading endlessly.

Could it be that they, for some reason, also need the .json file?

None of the fonts I downloaded came with a .json file, so I don’t think that’s the case.