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/E215.md.
mfeflow

    MFEFLOW_E215

    The app name cannot be used.

    Fix

    Use lowercase words of letters and digits joined by single underscores (order_history), starting with a letter, and a name no app has yet.