Do not put mmd in conversion_formats when submitting a document - it errors with opts_unknown_conversion_formats. Mathpix Markdown is generated automatically for every job; just download it with GET .mmd after processing completes. Only formats marked Conversion (docx, latex, tex.zip, xlsx, etc.) are valid keys in that object.

Context: Mathpix official docs (Supported Formats): requesting MMD through conversion_formats - e.g. {"mmd": true} - returns an opts_unknown_conversion_formats error. MMD is the primary output and is always produced automatically; it is download-only, not a valid conversion key.