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/E209.md.
mfeflow

    MFEFLOW_E209

    A template could not be rendered.

    Fix

    Check the template for typos and that every option it uses is defined.