The PDFCoraUI reference needs a web server

You opened it from the filesystem. The iOS references are built with Apple's DocC, which loads its pages with JavaScript from absolute paths, and browsers do not allow that from file://. Serve the site folder and open the reference from there:

cd site
python3 -m http.server 8000
# then open http://localhost:8000/developers.html#reference

The Android, web, Node and Java references are plain pages and open from disk.

The site is being served from the wrong folder

This reference was built to live at , but it is being served at . DocC looks for its scripts at the first path, so they are missing and the page would stay blank.

Serve the site folder itself, not a folder above it:

cd site
python3 -m http.server 8000

Deploying under a sub-path instead? Rebuild with the path it will live at: PDFCORA_DOCS_BASE=/your/path/api ./scripts/make-docs.sh --site