For AI agents: the complete documentation index is available at https://mfeflow.github.io/mfeflow/llms.txt, the full documentation bundle is available at https://mfeflow.github.io/mfeflow/llms-full.txt, and this page is available as Markdown at https://mfeflow.github.io/mfeflow/errors/E403.md.
mfeflow

    MFEFLOW_E403

    The registry's index.json is not valid.

    Fix

    Ask the registry owner to rebuild it with mfeflow registry build. It lists items with a name, version and description.